I think hypnosis tapes can be very helpful to a person who is trying to lose or change a bad habit.
You don't need to have a tape. There are plenty of books available about self-hypnosis. Some of them have to do with weight loss. Some have to do with breaking the nicotine habit. They work the same way: reinforcing your resolve when you are in a very relaxed state.
You also have to have the discipline to continue using the technique until it works (or doesn't) for you. In my area, there is a psychologist who offers hypnotism sessions to stop smoking, etc., in his office. I think that there is more than one session required to break a habit using his suggestions under hypnosis. I also know that hypnotism does not work for everyone.
However, if you trust psychology and a psychologist who is qualified, every little bit helps! Sometimes, it's just the thing you need. Years ago, when I went on a very low calorie diet, a small group of us dieters sat in a darkened room with a nurse and she gave us what I can only describe as hypnotic suggestion. The diet was very difficult at first but think that session helped us all to get through the early stages. So, yes, I believe hypnosis is a good tool for dieters!