IPL works quite well "IF" you use it regularly and as directed. I experimented to prove its efficacy to myself by NOT treating two areas, and the treated areas have been nearly denuded of hair. Three +/- months in using the IPL, after more than a week of not shaving and comparing the two non-treated vs the treated areas, the treated area is visibly smooth while the untreated area has hair growth as usual.
My iPL corded device bought on Ebay was inexpensive at ~$90 (now over $250 likely due to COVID
_ ) and I read that the "better" brands have upwards of 300,000 (some unlimited) flashes in their flash bank, while the less expensive had significantly less. As far as the really expensive models go, I only own one IPL and since mine was relatively inexpensive and it works I have to say that I'd go for any model with a high number of flashes in its bank under $100 WITH a replaceable flash module. I've used mine quite a bit and still have over 250,000 flashes in my bank.
Aside from that, from what I have read a big difference in the cost is the recovery time between flashes. Some can flash continuously reducing treatment time significantly, while others like mine have a 2-3 second "recharge" time necessary between flashes. Treatment time can be quite long if you're trying to remove chest, arm AND leg hair so that's something to consider in buying one. I'm only working my chest / neck areas so it's not a huge expense of my time.
Beside duration there "may" be a difference in minimum to maximum light intensity between the less expensive to the most. If some ARE more powerful, I'd likely use the lower powered settings as too much intensity can be quite uncomfortable. I use mine at what would be the 80% setting and it's just under my threshold of pain vs. comfort and it is effective. Also the actual area the flash covers "may" be larger on more expensive models.
The one "gotcha" is the method the IPL uses to "sense" when it's actually in contact with the skin. I mean it wouldn't do to be flashing it while waving it around burning the retinas of folks nearby
(or themselves) would it? Don't laugh, we live in a time where stupidity is rampant and society goes through great lengths to protect users and others from the stupidity of the perpetually stupid.
At any rate, mine has a thin "contact" pad and a mirror system that presumably performs the function of assuring skin contact before it will discharge. These areas (at least on mine) need regular wiping of skin oils and dead / burned skin flakes to keep it firing.
Two last things... I've tried cleansing the skin with witch hazel before treatment and it seems as if the discomfort is greater on the cleansed skin. Whether this is more or less effective at reducing / killing the hair root is not known but I alternate treatments using both methods. In either case I always wipe the treated area with witch hazel afterward. Also there are a few cordless models out there but this type of device generates an intense pulse of light and I may be wrong but I can't see how a cordless model can generate sufficient power for the average treatment time.
I have not read of these issues and I hope they answer any questions y'all may have.