I just got it at a local dermatology clinic.
I clenched my jaw and thought I had quite a lot of jaw muscle, so I got it, but I don't think I saw much of an effect. I don't have the courage to get double-jaw surgery, so I'm just going to accept it and live with it.
The price is low and they say side effects are rare, so if you're interested, I think you can try it once, and if you like it, keep getting it; if not, don't, and if it's not enough, get surgery. I didn't see an effect, but it's a decent procedure you can try without much burden, and if by any chance you hit the jackpot, it could be amazing.