I have only anecdotes, but I have met a lot of people with some form of HPPD even after moderate and safe usage. I think it is probably a bit underestimated right now. My guess is that it is one of the bigger risks of using psychedelics, along with PTSD from the experience and DP/DR. Andrew Callaghan of Channel 5 news has it pretty strongly but he did abuse it at a young age. He spoke about it on "therapy gecko".
Obviously the benefits is a fleeting and difficult to pin down thing. Outside of a clinical setting, experiences with psychedelics range from life-changing to life-destroying, with most people seemingly in the middle with "it's just fun". It certainly does not seem reliable.
I have DP/DR induced by LSD and I am always skeptical of psychedelic usage in psychology. I think that especially people with psychological problems to begin with should not be taking LSD or mushrooms. Even it's a small minority who get HPPD it's potentially life ruining.
I also have minor DP/DR and HPPD induced by very minor LSD usage years ago, which comes and goes depending on the situation. I've had times before where I literally start tripping, just for a moment, like I totally enter the trippy headspace or have a very trippy feeling. For example I will be cooking and suddenly the barrier between me and the food disintegrates and I just feel completely whack for a while. I also have lost a sense of what is in my peripheral vision, for example I was in a meeting earlier and in my periphery someone's bag fell over and I was convinced for a moment that it was an animal even though we were just sitting in an office. This happens basically every day and slowly getting worse tbh and I'm convinced it is an LSD thing. Also sometimes if my mental health is bad I have tactile hallucinations, like someone is tapping on my shoulder but no one is there.
I had actual HPPD for about a year after my trip, e.g. I could reproduce certain visual effects by looking in a certain way. I think it also caused my tendency to experience pretty strong open-eye hallucinations while meditating, which are called "makyo" in Japanese.
Of course, maybe none of this is due to the LSD usage, but I think some of it probably is.
After my 2 LSD trips with 100ug and very good setting (and I thought at the time good enough set) I slowly became very depressed and suicidal and had a total crisis. I actually had to seek out religion (which I always hated as a life long atheist) to be able to cope and not kill myself. It got close at some point and basically every since suicide has been lingering over my head. It made it a possibility: before LSD if I had stress I would lament at the world being unfair or something, after LSD if I have stress (even just minor work stress) I just can't stop thinking about killing myself. I'm on a waiting list for therapy but it is very long.
The absurd part about the LSD community is that even after telling other psych users all that, the response of about 50% of people is that I should take more at a higher dose...
Obviously the benefits is a fleeting and difficult to pin down thing. Outside of a clinical setting, experiences with psychedelics range from life-changing to life-destroying, with most people seemingly in the middle with "it's just fun". It certainly does not seem reliable.