I have often seen those weird powerbuilt sockets and wondered if they actually worked. I love my rattlegun and 6 sided impact sockets for suspension work.
Depending on how much access you have to the stripped nut, i would try a few things myself. Hammering on a smaller socket, a hammer and chisel to try and turn it (or cut it off), or just plain old cutting it off with a death wheel or dremel.
I see a few of these around too and also wondered if they work for cutting off rounded nuts. Havent really needed one so far.
You can get these from bunnings too, seem to be rated fairly highly (although once again havent had a need for them myself). They use a reverse spiral so they get tighter as you try and loosen them.