could be state law dependant(i dunno where you're located), could be that they are NFA regulated as title II / class III AOWs(any other weapons) and therefore subject to additional laws in your state(if they are illegal to carry in your state)... AOWs include things along the likes of large bore pistols, cane guns, zip guns, knife guns, wallet holsters(standard handgun must be registered as an AOW to use in a wallet holster iirc)etc.
I do not believe they are illegal to carry in most places providing they are properly in the NFA registry as an AOW ($5.00 tax and blue-stamp).
hrmm, i may have to go back and look but iirc it's a $5 transfer on those and large bore pistols(serbu and safety harbor, etc. shorty shotguns[not sbs]), but a $200 manufactureing tax. though that should just be built into the price of the item... K.
