I got one from Bushmaster, really had no use for it other than it looked cool, but then it doesn't look like the 40mm version, too much metal between the tube/trigger and the rifle barrel.  The one I got had some wrong sized pins for mounting, I ended up hammering them in the holes.  Bad idea, when I wanted to take it off my rifle I had to hammer them out [pissed]  The instruction is terrible, seems to have been copied on a cheap fax 2000 times before I got it.  It also made the rifle very heavy.  Unless you have a real use for it, in which case just get a small flair pistol, in my opinion you'd be better off without it.  Just my two cents.

Yeah your 37mm looks a lot better than mine when mounted, I just learned not to blow money on stuff I can't really use.  For close to $200 I can get other cool stuff I actually can get to enjoy or use it as a down payment for a better scope.