Not only do certain brain wave rhythms get strengthened as a result of entrainment, but a dominant frequency band results in a different state of awareness. Those that have used a quality brainwave entrainment product can vouch for the fact that their perception is altered by their brain waves. Not only could this be due to brainwave changes, but it may be a result of increased interhemispheric communication.
Deep relaxation is a major benefit resulting from the brain’s cortical frequency following response. By selecting the desired rate the brain, via the frequency following response, will tend to mimic the rate it is exposed to and thus enter that brainwave state. This helps to explain why this technology can produce benefits commonly found with meditation. One of the most valuable benefits of consistent  brainwave entrainment is that we are able to experience and recognize the various states of consciousness. With practice we can learn how to re-create these states.
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.

Because each track is specifically aimed at attaining a certain outcome, you can pick exactly which track you want for what you want to do. This is great for beginners because you can start off with some simple tracks such as Instant Energy Boost or Endorphin Release. And then if you find you like them you can choose some of their more hardcore stuff (such as Lucid Dreaming or Shaman Consciousness).

At the end of just two weeks of use (I was now into the Equisync II cds), I experienced for the first time ever, what my partner described as Nirvana. I experienced a complete dissolution of individual consciousness, felt at one with everything, and felt the deepest peace, love, and complete bliss I had ever, ever experienced in my life. Since you do all the research on this, you know what I’m describing. Unfortunately, language does not express it. I have never experienced mind altering drugs, but I recall watching a documentary of LSD research, and one of the subjects described the exact same “feelings” as I had when she had received a micro amount of LSD.
What I really like about iAwake is their standalone offerings. They produce quite a few audio pieces that are geared toward specific brainwave targets and desired results. These individual products aren't progression - based (you can listen to whatever tracks you want whenever you want), so there's no lengthy investment of your time involved. Also they're way cheaper (around $30-$50 depending on the product). In addition to manipulating brainwaves with sound, they pride themselves on their patented Biofield tech (look them up for more info).
Kelly Howell brings 30 year's experience to her expertise. She has been cited by the Mayo Clinic as "renown for her pioneering work in healing and mind expansion (and) visionary recording techniques." She has collaborated with neuroscientists and biofeedback therapists to invent a sophisticated sound recording technique that makes Brain Sync programs more effective. The result is the most elegant and effective brainwave synchronization audio programs available in the world today. You'll feel the effects from the very first time you listen. With regular use, you'll establish new healthy patterns that last. Brain Sync programs use window frequencies – extremely precise frequencies that fit through narrow biological windows to impact the body at the cellular level. The choice of frequencies selected for each program is based on biofeedback research. Programs are designed to help you self-generate optimized brain states exhibited by remarkable men and women.
I have received many requests for live sessions and personal support via telephone and video chat (Skype or Facetime). I am proud to announce that you can now schedule your own appointments with me for personal consultations, hypnosis sessions or any general counseling, questions or concerns about your specific needs, life coaching, self-help issues, dream guidance, spiritual matters or just random questions about consciousness or reality in general. I look forward to speaking with you on the phone or video chatting via Skype or Facetime.

I like it. I like the fact that I can just sit there and observe my thoughts and feelings and then go back to watching my breathing. It really does teach me to be centered and balanced. I look forward to the next several weeks. By the way, what I am doing now is meditating for 23 minutes in the early morning and again 23 minutes in the early evening. I’ll check back with you.
However, yoga and meditation take time to learn and master, and until the student becomes proficient, progress can be slow and frustrating, leading many people to abandon the effort before they see the benefits. Brainwave entrainment has the potential for helping a person enter the relaxing and rejuvenating mind-states brought about by yoga and meditation without the learning curve and time needed for mastering these other techniques. Brainwave entrainment may even facilitate learning other mindfulness methods by helping a person achieve success faster and more reliably. 
The specific benefits and claims from this technology are often disputed and considered scientifically questionable. One problem is that there are few experiments that have utilized brainwave entrainment for the purpose of treating a specific psychological ailment (e.g. insomnia). And the experiments that have been conducted are largely backed by corporations that sell the software; hence it could be speculated that there are conflicts of interest.

Hemispheric synchronization: Whether it’s optimal or suboptimal to operate in a state of hemispheric synchronization remains unknown. Some speculate there are numerous benefits of brain waves operating in “sync” as a result of entrainment. There may be an increased communication between the right and left hemisphere of the brain – which could improve certain functions. However, it is also important to realize that increased hemispheric synchronization may not be as beneficial as many have speculated.
I’ve been using equisync first thing in the morning after I get up, and listen to all three tracks in a row. I again listen to all three tracks in the late afternoon. If I don’t have that much time available, I will start on Track 2 or 3, as necessary. I have really started to focus on my breathing, and notice the difference – I finish the session in a DEEPLY relaxed state.
EquiSync’s design is based on the 100’s of studies performed on the effectiveness of brainwave entrainment technology, and 1000’s of studies on the powerful benefits of meditation. If you are interested in better understanding the power of this technology and rapidly expanding field of research, then here is a very abbreviated bibliography, a very small sample of the studies out there:
Ultimately the only way to know if this is right for you, or if it works for you is to test it. A good audio creator should be willing to let you give their audios a test drive to see if it’s right for you. When you test this type of technology, one that is largely left to subjective experience, I would highly recommend you listen to the same audio daily for a full week or two, taking one day off per week. There are many different experiences that can be had with this type of technology, including not noticing it doing anything at all. Having at least 5-10 experiences with it will give you a reliable way to gage whether or not this is going to work for you.

The functional role of neural oscillations is still not fully understood;[6] however they have been shown to correlate with emotional responses, motor control, and a number of cognitive functions including information transfer, perception, and memory.[7][8][9] Specifically, neural oscillations, in particular theta activity, are extensively linked to memory function, and coupling between theta and gamma activity is considered to be vital for memory functions, including episodic memory.[10][11][12]