I'd love to have one in my toy closet, both for girlfriends and maybe for myself, but it's way out of my budget.
And they seem to be quite noisy. The ones I've heard in porn clips sound like a washing machine on spin cycle with bath rugs in it.
That said, they seem to do quite a job stimulating the user until they are simply overpowered by it.
Another interesting application is using it for prostate massage as well, as demonstrated by this male "milking" site.
You can see these guys can barely stand up and climb off of it afterwards.