Isochronic tones work just the same in delta as they do in alpha, theta and beta and they are widely used in the brainwave entrainment community to help people sleep. Like you, I’ve also seen some websites saying they don’t work in delta, but it’s a bit like the game of Chinese Whispers, where someone makes a comment and then after it gets passed around and shared a lot the message gets distorted and appears to be a fact. I don’t know of any scientific reason why they wouldn’t work in delta. I remember some people talking about this on a brainwave entrainment forum many years ago. They were saying they found isochronic tones a bit too abrupt for using to help them sleep and they preferred binaural beats, as they thought they were a more soothing sound. That was just a personal preference shared by a couple of prominent forum members at the time and some people then took that as a fact for everyone. That’s where I think that belief originated from.

Brainwave Entrainment is the process of synchronizing the brain to specific frequencies and patterns embedded in audio tracks. These frequencies correlate to specific emotions, feelings, and even energy levels. Using nothing more than sound, Brainwave Entrainment can enhance creativity, change moods, and even alter behavior like sleep and energy levels.
In the 1980s, a researcher in Japan, Tsuyoshi Inouye described how light stimulation creates synchronization of brain hemispheres. Since then, other researchers have detailed the positive effects of hemispheric synchronization including a 1984 study by researcher Dr. Gene W. Brockopp stating that hemispheric synchronization resulted in improved intellectual functioning as well as improvements in long-term memory, and these effects are cumulative over time.
So, in summary, binaural beats certainly do not work the way the sellers claim, but there's no reason to think they're any less effective than any other music track you might listen to that effects you in a way you like. If they make you sleepy (like they all do for me), use them to go to sleep. If they relax you or get you amped, use them for that. But don't expect them to be any more effective than regular music. If someone you know claims that they are, put them to the test, and bust the myth.
Meditation is the practice of calming the mind and tuning down the number of random thoughts that pass through it. A regular meditation practice has been shown to reduce stress and anxiety, slow down the rate of brain aging and memory loss, promote emotional health, and lengthen attention span. Practicing meditation regularly can be quite difficult, so people have looked to technology for help.
Brainwave entrainment through the use of binaural beats is a scientific method that helps you go from alert to relaxed to asleep within minutes by using a process to alter your brainwaves. Sounds like something straight out of a science fiction novel, but brainwave entrainment is a very real and very effective way to help you sleep. Your alertness is linked to the dominant frequency of your brainwaves. So if you’re feeling alert and focused, your brainwaves are in the beta frequency but if you’re feeling relaxed, they’re likely to be in the alpha state. To sleep, your brainwave frequency needs drop to a slow delta. This can be hard, especially after a busy day. Your brain stays alert, preventing you from relaxing. By using Binaural Beats, you can quickly induce the frequencies associated with sleep in your brain within minutes.  Scientists discovered that the brain synchronises itself to a dominant frequency. So by inducing a new lower frequency with binaural beats, your brain begins to lower its own frequency to match this new frequency. It’s a powerful technology that I’ve been using myself for years with very good results.
Completely free of spoken words, this program delivers a unique combination of Alpha, Beta, Theta and Delta binaural beats that produce an extraordinary “mind-awake/body-asleep” state through brainwave entrainment. Negative thoughts are dramatically swept away by brilliant flashes of insight and understanding as you experience untold depths of inner peace.
Because of the way they are created, there may be a positive benefit from listening to binaural beats without considering the brainwave entrainment aspect, but I haven’t seen any research on that. I first discovered brainwave entrainment through binaural beats about 10 years ago now, but they didn’t do anything for me. So I’ve never been a regular user of them. I believe isochronic tones are a more effective way to produce hemispheric synchronisation because they produce a much stronger response in the brain
The gentle pulsating rhythms of Brain Sync audio programs act in a similar fashion, yet because the frequencies are precise and consistent they can be targeted to induce highly specific and desired brain states. Just as you can tune a radio to get a particular station, with Brain Sync technology you can re-tune your consciousness – effectively dialing your mind into a wide variety of brain states.

This syncing of frequencies is a not a new phenomenon. In fact, it happens within our bodies every minute of every day. Slow down your breathing, for example, and your heart rate and brainwaves slow down to match. The reverse is also true, which means that by slowing down your brainwaves you can affect your heart rate and respiration, thereby inducing the perfect state for effective meditation[3].
Did you ever wonder why someone who "has everything" could be depressed and unhappy and why someone who has very little can be so happy? Of course, we can answer that material wealth, beauty, situation, good environments aren't everything. (Sure are nice though :+)) But that explanation ends up seeming like a rationalization and not an explanation. Consider the idea that the answer could reside in our brainwaves. Certain brain frequencies promote a feeling of well being and certain frequencies promote a feeling of depression. The state of our brainwaves also influences our tendency to be overly reactive or detached.
The I-Doser claims it can emulate prescription drug-like effects by listening to MP3's, to get stoned.[1] This is largely a moral panic by parents who flunked science fueled by the eternal quest by teenagers to get stoned, and stupid ones convincing their friends it works. It is really more of wishful thinking and making yourself disoriented by playing discordant sounds really damn loud. If you want to experience it yourself, you can always listen to Bjork Captain Beefheart dubstep.
There is a lot to like about this technology as a potential treatment for sleep problems. It’s low impact and non-invasive, it doesn’t rely on chemical drugs, it’s inexpensive and for most people likely easy to adopt and maintain. In this way, it’s similar to the other behavioral therapies for sleep that I like so much, including meditation and relaxation techniques, and other mind-body therapies.
... One of the possible explanation for insignificant results could be length of exposure to AVS. Our participants were exposed to it for 11 minutes, while some authors (Cruceanu & Rotarescu, 2013) suggest that at least 20 minutes is needed for the positive effects to take place. Furthermore, part of our reserach was also visualization of gymnastic skills, performed after AVS. ...
Cortisol is an arousal hormone, stimulating alertness and attention. Cortisol levels rise and fall in connection to circadian rhythms—cortisol levels rise to their peak levels first thing in the morning, just in time for you to be active for the day. Too-high cortisol levels are associated with insomnia, as well as more time spent in light sleep, rather than deep sleep.

Brain wave entrainment is a real phenomenon and is useful as one method of investigating how the brain works. But there is no evidence, nor any theoretical basis, for any long lasting effect on brain function or that there is any benefit of any kind. Despite this, there is a huge industry of devices that claim to train your brain waves and have a beneficial effect. I wouldn’t waste a dime on any such device.
Over-arousal in certain brain areas is linked with anxiety disorders, sleep problems, nightmares, hyper-vigilance, impulsive behaviour, anger/aggression, agitated depression, chronic nerve pain and spasticity. Under-arousal in certain brain areas leads to some types of depression, attention deficit, chronic pain and insomnia. A combination of under-arousal and over-arousal is seen in cases of anxiety, depression and ADHD. more...
Brainwave entrainment through binaural beats is a powerful way to alter your brainwaves and induce deep sleep. Perfect if your mind is full of thoughts, you’re suffering with any anxiety or you just want to get to sleep fast. And unlike sleep medication, they’re completely natural and the quality of your sleep is likely to increase with use, not decrease.
♥ At 56, I have tried many a thing. The default setting of Binaural Beat Machine does make me very relaxed. But it's not what it does on the moment, pleasant as this might be. It is the quality of the sleep, when I use it for half an hour before going to bed. I sleep a deep, restful sleep. I use it during day-time meditation as well, and the clear-mind feeling about an hour later is wonderful!
Slightly higher-frequency entrainment can lead to hyper suggestive states of consciousness. Still higher-frequency EEG states are associated with alert and focused mental activity needed for the optimal performance of many tasks. Perceived reality changes depending on the state of consciousness of the perceiver (Tart, 1975). Some states of consciousness provide limited views of reality, while others provide an expanded awareness of reality. For the most part, states of consciousness change in response to the ever-changing internal environment and surrounding stimulation. For example, states of consciousness are subject to influences like drugs and circadian and ultradian rhythms (Rossi, 1986; Shannahoff-Khalsa, 1991; Webb & Dube, 1981). Specific states of consciousness can also be learned as adaptive behaviors to demanding circumstances (Green and Green, 1986).  
As somewhat of a modern mystic, I have studied altered states of consciousness, but due to my monkey mind, I have only been able to experience them to a very minor degree. I have tried so many methods of meditation to little avail. But I became aware that I would not be able to progress in my spiritual life if I could not achieve at least a modicum of success in meditation.
Cvetkovic D, Simpson D, Cosic I (2006). “Influence of sinusoidally modulated visual stimuli at extremely low frequency range on the human EEG activity“. Conference proceedings : … Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 1: 1311 – 4. doi:10.1109
Electroencephalography (EEG) has been used in many studies as a primary method for evaluating the meditating brain. Electroencephalography uses electrical leads placed all over the scalp to measure the collective electrical activity of the cerebral cortex. Specifically, EEG measures the electric fields of large groups of neurons. EEG has the benefit of excellent temporal resolution and is able to measure aggregate activity of portions or the entire cortex down to the millisecond scale. Unlike other imaging based methods, EEG does not have good spatial resolution and is more appropriately used to evaluate the running spontaneous activity of the cortex. This spontaneous activity is classified into four main classifications based on the frequency of the activity, ranging from low frequency delta waves (< 4 Hz) commonly found during sleep to beta waves (13–30 Hz) associated with an awake and alert brain. In between these two extremes are theta waves (4–8 Hz) and alpha waves (8–12 Hz).
Beta – Throughout the day our brains are in the beta range with a frequency of about 13hz and up. At this level we are active, busy, and all our emotional responses are at this level. People who are over active, or often depressed, irritable, angry etc., often lose out on the recuperation and recharging that takes place when we are relaxed in the alpha, theta, and delta levels.
How does acupuncture work? Acupuncture is an alternative therapy that involves inserting thin needles into targeted areas of the body. Some believe that this balances a person’s vital energy, while others point to a neurological effect. Acupuncture may relieve pain and a range of other symptoms. Here, learn about uses, risks, and what to expect. Read now