OK, I've used both, and I *cannot stand* HPP. To be fair, I was using Prozac(tm) at the time, which does prevent hypnosis. Mainly, as a person with a brain and ears, I was a little upset about the way the "hidden messages" came together. It would break the trance state (if one could be said to have existed), and I'd find myself bored at best and upset at worse.

One thing I recommend is first checking your library's catalog. These tapes have been around a while, and have been resold by a few NLP/self-help companies. If you like it, use it.