i have one. The literature included instructs you to lube well and insert- the blunt rounded shape inside presses right against the prostate directly and the other rounded hook area stimulates the perineum (taint.) Its a constant (teeter/totter) see-saw type action reaction, and the anal muscles will release to expel which rubs the contact areas which causes contraction which draws it in and pings the prostate inside, then repeat... if you leave it in for a few hours eventually you are supposed to give into an orgasmic meltdown of mind-bending proportions...
I don't think i have ever had something like that happen- but I will say that it does put more pressure on the prostate, so that orgasms are more intense. Like constricting a garden hose, you can increase the pressure without having more water... so if you're alone and just getting your rocks off it can be a more intense time.
I'd say the shape and size are well-determined so even a person who doesn't do a lot of insertions (or enjoys it) will do fine with it.