Magazine is short, and only holds four rounds. Lots of WB stages shoot 6 shotgun targets. I would feel at a disadvantage shooting that rather than a full length magazine, which can hold 6 rounds of 2 3/4" shells (sometimes with a little work and a couple of parts).
So - legal? Yes.
The wise choice? No
Generally there are a lot of regular Model 12s around. Because of that, I'd go the conventional route and get a standard M12.
good luck, GJ