It's name sums it up appropriately. However, it actually does work--it is not a scam--although for the time it takes to install, you might as well try and find a real diff.
Having used one (and later a quaife), I can say that there is nothing you will really notice about either of them (other than lap times). A dramatic seat in the pants kicker diff is, of course, the locker or 220V model.
Cheers.