To me, self hypnosis is just another form of meditation, and it can work well to counter stress or anxiety. The instructions in this book are pretty clear.
As far as practical results: Like I said, it helps with relaxation. I can't say I've felt as if I were completely in some kind of trance, nor have I tried to use hypnosis to help reach specific goals, like losing weight, so I can't comment on how effective that might be. I do know at least one person who claims to have been able to stop smoking immediately and completely after hypnosis (although not self-hypnosis). There was a legendary guy here in Boston some years back that people called The Mad Russian. I don't know his real name. He claimed he could break people of the smoking habit through hypnosis. A woman I knew, and considered trustworthy, said she went to him and it worked. I went to a relaxation workshop where the the instructor taught the group some hypnosis techniques, and they seemed to have an effect. Placebo effect, maybe? That experience was what got me interested in learning more about hypnosis, though.
The authors do seem to endorse a few dubious claims/practices, such as neurolinguistic programming (which I know little about, but am not sure if it's really a thing--hence I say "dubious"). When they say you can use hypnosis to clear your skin, that makes me wonder. Maybe it would help if stress was a cause of the breakouts. But I tend to think they make too many claims about what hypnosis will do for you.