IMHO - I have used hypnosis therapeutically (mostly for pain control) and am a big advocate. I also know and use self-hypnosis for many different reasons, including sexually. BUT (and this is a big BUT), the indiscriminate use of and for especially sexual situations by someone who may or may not be trained and licensed is playing with a loaded gun - not just Russian Roulette as all chambers are loaded. There is a lot of damage which can occur and be caused in this sort of situation.
If he is trained and licensed this is a strange way to proceed. I think it panders to those who have much greater expectations of gratification than are realistic and can be dangerous. Remembering, even hypnosis CANNOT make you do things you would normally not do, but it can release some inhibition, esp. with post-hypnotic suggestion, and really fuck you up!
Again, IMHO.