I've done about 15 HFO hypnosis audios, and the overwhelming response I've had to them is that they work. I joked about 'collecting' HFO's at one point because every comment was about how the listener had achieved his first HFO.
In writing and performing so many of them, I've sort of pinpointed two things that I think are crucial to a successful HFO audio/experience, and which are often lacking in some scripts or performances.
The problem with many hypnosis scripts and experiences is that the listener is not given (or gives himself) enough time to adequately reach this state of relaxation. This is called the 'induction' and to be really effective, it should take at least 10 minutes to perform, using a sing-song voice, slowing down, incorporating relaxation and breathing, full body muscle relaxation etc. Then the script/listener should provide for another 5 to 10 minutes of a 'deepener' - an image of a staircase or an elevator or a countdown of some kind....even slower than the induction. Guiding the listener through the imagery of sinking or going down into deep relaxation. And only then, after a solid 15 or 20 minutes of dedicated effort on this, should the script/listener attempt to guide towards the sexual stimulation. An HFO script should be about 50 minutes start to finish, and a lot of people aren't able or willing to put that kind of time in. Binaural is an option, but it requires a lot of editing skill (it has to be seamless, or it will jar the listener out of trance).
Some people are afraid they are 'doing something wrong' during it, that if they touch themselves the 'spell' will be broken, etc. This isn't the case. Hypnosis is really just deep relaxation, you can move, touch yourself, etc if you want to. But with practice, a lot of men find that they enjoy the kind of weightless sensation they can feel during hypnosis, and find that their minds and the woman's voice alone are capable of bringing on an orgasm without touching. A lot of guys benefit from edging quite a bit beforehand, even to the point of denial for several days or a week, just to be more likely to HFO.
And of course there is a kind of 'performance anxiety' that comes with it - many men become anxious even before they hit play, worrying that they will fail at this and won't achieve it. Anxiety is a definite boner killer, so it's best to go into these audios without any expectations. Maybe you'll have an HFO the first time, maybe you never will (all men respond diffrently), or maybe it will just take getting used to. I have reminded listeners that maybe they experienced wet dreams when you went through puberty - if so, this is something you know your body can do. You're just going to help it along this time.
But anxiety should never be a part of it. Whatever you get out of the audios, they are a pleasant, arousing, relaxing experience.