Know the things you mean there was one at school but I'm afraid I never used it.
Only thing I would say is that if its battery powered avoid it. They have to be on for a while and if it wasn't mains powered I would imagine it would eat through batteries. The school one was main powered and to be honest the only people I ever saw use it was the girls.
Is there a craft shop near you? Perhaps you could get a demo. I have seen some stones beautifully polished up and while it doesn't appeal to me at all I can see that it could be an interesting hobby for some folks, and its an unusual gift.