You can learn about Zengar on
http://www.zengar.com . There is a list of practioner on the website. There is a very good one in NYC.
After four sessions, I feel better overall. I am calmer and can cope more effectively with my messy situation related to my employment. From the psychologist of the Zengar treatment a very interesting aspect came out. He explained that release of old emotional traumas can only take place at about 7 Hz frequency (upper theta, near alpha). From my further questioning and my own initiative, it came out that the crucial release frequency is actually 7.83 Hz, the Schumann Resonance (ie the frequency at which the earth vibrates). The psychologist confirmed my inference as he had asked the same question at a Zengar workshop to the inventor of the method.
The problem is that, if brain entrainment makes you produce theta waves below 7 Hz, all you do is bringing up unprocessed old emotions, feel uncomfortable and send them down again. This process can repeat itself forever, unless you can hit the magic 7.83 Hz. I have not explored how our environment affects this frequency. For example, if the electro-magnetic currents around our house (NB we all have power in our house, offices, etc) create some unknown effect which affects the Schmann Resonance, we may not be able to stay at 7.83 Hz or around it long enough for us to release these emotions. So we will be stuck into our problems forever without knowing why. Of course, this is just my speculation.
I still believe there is merit in brain entrainment. Holosync is one of the best known products on the market to assist in producing long term effects. What beats me is that I have never heard testimonies from people who have completed the program. Bill Harris has. Well... it is everybody's decision to form an opinion about which effects it has had on him.