Marc:
I've checked one out at our club; being a stockmaker I already had similar tools, but this is pretty much an all-in-one deal. Also was set up next to Bob at the Stamford, CT gun show, so I heard every detail. It is a pretty useful tool. The extension has a magnet in so the unit will sit on the rib and you can have both hands freed up to adjust and check measurements. IMO, though, unless you are really into the "+/- 1/32 of-an-inch" realm, it may be a bit of extravagance. Hope this helps.