My experience as a skeptic over the last ~4 years of listening to many, many files. I'll just put the results at the top and tips below.
Results:
I've become very good at wetting diapers without thinking about it. Once I'm in a wet diaper, not going automatically requires concentration. Additionally, when I put on a diaper I'll feel the same conditioned need to go that one might when entering the bathroom. It has also broken down barriers around messing; I'm one of those "messing isn't for me" people, so that was a surprise. It has also genuinely helped with flattening binge/purge cycles.
Those are the only "real" impacts, but it's been plenty of fun along the way. On some level, I wanted all of those things; I feel like hypnosis was just an avenue to get different parts of myself on the same page.
I think those describing major changes, especially online, are full of shit. The only way I can see hypnosis causing major change would be participating with it in-person so they can adapt their approach, with someone you genuinely trust, and with agreed-upon intentions. From files? I sincerely doubt it.
Tips:
If you want hypnosis files to "work" in any capacity, you need to practice falling into trance. If you haven't ever been in a trance in response to a file, try finding different inductions. Worrying about whether you're falling into trance or not during a file is a pointless distraction; just focus on the audio. Once you learn to trance and learn to recognize you're in trance, hypnosis is a lot more fun.
The first time I find a file I'll listen to the suggestion portion in its entirety. From experience, if I'm in a good trance and I hear a suggestion I think is ridiculous it'll drag me out of it immediately. Sometimes I'll still listen to files with ridiculous suggestions, but I expect nothing to happen and have never had anything happen. It's more like a guided relaxation / fantasy with no lasting impact. Most of Dosei's files fall into this category for me, and Hypno-Mommy has files intentionally in this category. They're fun but not typically what people think about when they think "hypnosis."
Audio quality and word choice matter a lot. It's especially distracting in trance if I can hear background noises (like a pet moving), or the hypnotist chooses words I'd never use. ChampTehOtter falls into this category -- I think his audio is high quality, but his word choices and emphasis is distracting for me. If you find a voice you like, with a style you like, and learn to trust their suggestions as what you want both fully alert as well as in trance, that's the ideal.
Fiona Clearwater's bedwetting files are about as good as file based hypnosis can get imo. Wish she had more diaper stuff. Vive has a lot of varying inductions, which is good for finding out what works. (Fiona Clearwater's is available in most hypno threads, including this one, and Vive you can just Google.)