The features in which you refer to are inclusive of teh birdcage FH which doubles as a Rifle Grenade launcher. This means that you can attach rifle launched grenades to it and fire a special blank cartrige and launch a grenade. The 37mm Flare launchers are 100% legal (except in Kali) to mount. Pre or Post ban. You cannot though own and projectile rounds such as bena bag rounds, fletchette rounds, (or adapters) and the shotgun adapters are really ilegal too, but that can get down to splitting hairs IIRC. But to answer your question on a Federal level the 37mm flar launcher is just that a flare launcher and not regulated under the AWB, NFA or any other Federal Firearms regulations as they are not viewed as a firearm or an accessory to such.