The Beauty of a bang stick as a killer is that it ALWAYS delivers a contact wound...
That means that not only are you pumping lead into the victim, but one helluva lot of rapidly expanding gasses... and it is those gasses alone that kill just as, if not more effectively as a bullet.
Ask Bruce Lee's son, Brandon.. he was killed on a movie set, from a gut shot with a blank pistol.
As far as being NFA, I'm not sure, it is certainly a short barreled, but it is not designed as a shoulder fired weapon, it is not really a handgun in the traditional sense, I dunno... Curios firearm maybe... got me.. I have seen them offered in Dive Shops, and they darn sure didn't have an FFL .... hummm...