Hi Julie! You’re very welcome for the info. In answer to your question, I think some are probably good, and some not so good. There are many people putting brainwave entrainment out there these days and it is not so easy to figure out which ones are and aren’t of reliable quality without investing time and doing some research. I would say (in general) that paid products are probably better quality than free ones, but I couldn’t guarantee this is a golden rule. My best advice is to just do your research before spending too much time listening to the freebies.
Discovered by Austrian Psychiatrist Hans Berger in 1908, Alpha brainwaves cycle 8 to 13 times per second, a good bit slower than beta brainwaves. While considered a part of a group of brainwaves, the Alpha brainwave has one distinct trait that makes it stand out from its siblings – it appears and disappears while going through our brain. Sometimes alpha waves are present, sometimes they are not. The disappearance of the Alpha brainwave usually occurs when someone is asleep or experiences heightened emotions such as fear or anger. This brainwave only appears whenever a person is awake and relaxed, a one-of-a-kind distinction among other types of brainwaves. 
Robert Monroe, a radio producer and executive published a popular book called Journeys Out of the Body about his out-of-body experiences when using brainwave entrainment. He later founded an original brainwave entrainment audio company, Hemi Sync. In 1981, the book Mega Brain by Michael Hutchison brought brainwave entrainment information, techniques, and terminology into the popular press.
The frequencies embedded into each NeuralSync™ audio integrate three audible tones with a fourth subliminal pulse. This inclusion of both audible and subliminal entrainment engages brainwaves far more efficiently than single protocols such as standard meditation practices, binaural beats or isochronic tones. Because this waveform is also balanced, it compels both sides of the brain into hemispheric synchronization much more easily and effectively than other methods.
At a certain point (generally after about four to six months), your brain will have made all the changes it needs to make to handle the Holosync® we use in Awakening PrologueTM. At that point you’re like a runner who’s been running two miles a day for several months, and now two miles is easy, because the body has created the physical structure that can easily handle it.
Insomnia: Perhaps one of the most promising uses of brainwave entrainment technology is for those struggling with insomnia. While the technology is unlikely to provide a “cure” it may help those who have a high level of arousal or are “keyed-up” – reduce their level of internal arousal and sleep. Specifically insomnia that is induced by excess stress (e.g. beta activity) would likely benefit from slower wave stimulation (e.g. alpha activity) to aid the brain in transitioning into sleep.
-Other Specialized Entrainment Methods: There are a few other things to consider like whether the audio creator uses binaural beats, monaural beats, or isochronic tones when appropriate for the desired effect of the audio. Or whether they use other entrainment methods as well, like volume modulation, pitch modulation, or panning from right to left of the headphones to further improve the immersion of the audio.

A few months ago I decided to test the ability of the “Equisync II” brainwaves therapy combined with other more traditional self-improvement programs and the results have been even more amazing to me. Currently in my mind I honestly believe this type of therapy can be a breakthrough, or simply the genesis of a new type of therapeutic techniques to correct several psychological, and behavioral human issues including depression, lack of organization, and self-esteem among many, many other possibilities.
Quick example: Brainwave readings (with an EEG machine) have shown that brainwaves of 2Hz occur when an individual is asleep. Scientists can create special audio recordings, which contain an encoded 2Hz frequency. While listening to such audio, the brain naturally follows (entrains) toward that 2Hz frequency, lowering its brainwave patterns. That's "brainwave entrainment." The net result is that when listening to such an audio recording, you (the listener) will naturally fall asleep.
Theta stimulation: There appears to be no benefit associated with using theta stimulation for cognitive functioning, mood, or stress relief. While theta may be a useful way to induce sleep or alter your state of consciousness, there really isn’t much science supporting entrainment in this particular range for most purposes. Photic stimulation of theta between 5 Hz and 7 Hz can be useful for headaches.
A very pleasurable experience during listening (and often for some time afterwards). As Holosync® changes your brain wave patterns to those of deep meditation, the brain produces several very pleasurable neurochemicals, including endorphins (the same endorphins responsible for “runner’s high”)…as well as several hormones with a profound and positive effect on longevity, aging, stress, and well-being.
The activity of neurons generate electric currents; and the synchronous action of neural ensembles in the cerebral cortex, comprising large numbers of neurons, produce macroscopic oscillations. These phenomena can be monitored and graphically documented by an electroencephalogram (EEG). The electroencephalographic representations of those oscillations are typically denoted by the term 'brainwaves' in common parlance.[4][5]
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