I have one I bought from Brownells, the dial indicator, same exact device, but I think it was less money. I like it, perfect for gun shows, just preset mine and lock at .350 with my electronic venier gauge and slip it into the bore. The legs are about 4" long, so you can get behind the choke and draw it forward and get the reading. And get the bore diameter 4" from the muzzle too
I have a brass step type plug choke reader, but it is useless at a gun show, or anywhere else as it will not tell you the bore diameter and some of the older guns have been severely honed.
Mike