I have a 12v versionThey work OK, way faster than the stock lug wrench! Still, I can use a 4-wayeven faster to spin them off, so I normally use the impact just for really stubborn bolts/nuts. It does not work like a pneumatic one, it kind of spins up for 2-3 seconds, then impacts. It takes about 3-4 of these impacts to get a lug nut off, so don't expect any stock car pit crew tire changing action out of it...
On the other hand, if you have one similar to thisit works just about as well as an air powered one.
On the other hand, if you have one similar to this