I did this 2.5 yrs ago, I went for a few sessions as it was £50 an hour - it was my second time of trying it - the first time I wasn't very motivated (back in the late 1990's). So I was really motivated the last time I tried - I dropped from 17 st 4lbs to 14st 2lbs - At first it was quite fast and it is strange how you just don't want to eat and are more mindful. Also it helped me make better choices more easily and exercise more. If you have a particular food you want to give up forever then you can usually choose to be programmed not to want it again - I didn't go down that route but some people do. I couldn't afford to go as I don't work and would have to ask my husband to cough up the dosh, but would recommend it.
I have also tried Paul Mckenna's CD on weightloss and it does work (for me). Perhaps you could try that first.
Some people are easier to hypnotise than other's so it may not work in every case.
I have just started to try to lose weight again as I put on 10lbs from my lowest with hypnotherapy and need to lose a couple more stones from there but if think back to my sessions and the things we discussed my head goes back to the good place and it makes me more mindful and motivated again.
I started back on losing weight 1st March and hope to report my success at the end of the month. One thing we did work on was not weighing very often as it wasn't good for me when the scales didn't move.
I am thinking about joining WW just for some motivation - hoping they will understand that I won't weigh or won't want to know what the scales say!