The only time I can see needing something like that is if I was doing a large number of plugs at a time. Other than that it seems like another "check me out" tool
I think that's the one Sport Compact Car reviewed. Their take on it was basically the same as Brian's. If you're only gapping four plugs, it's more trouble than it's worth to just get it set up right. If you're gapping a whole fleet's worth of plugs, then it could be worth it.