Troy basically building a "firearm" with a brace, VFG and OAL greater then 26". It's a "firearm" under the law as it has a VFG as it's designed to be fired using two hands. Take off the VFG, it becomes a pistol and illegal in those few states. Troy produced a firearm that was OK'd by NJSP and is/was allowed under NJ laws. It even came/comes with a legal letter, accepted by NJ, and the Troy lowers are marked "Other". The 12.5" barrel does not have to be pinned as it gets it over the 26" OAL without the flash hider. Are NJ anti-gunners groups and government going to fight it, of course, and already are or have as I haven't heard or looked into that fight. Anti-gunners and even some pro-gun idiots on YouTube are calling this-type of build/firearm a "loop-hole" gun, which it is not. The "firearm" or "other firearm" has been legal everywhere else all along, allowed under federal law and by the BATF well before Troy and some others started building them. I'm not from NJ, don't know their current laws/situation or if this has changed since the middle of last year (June-July 2019) when all this came up in NJ.
I'm sure you know but for others, anything 26" and under with a brace, pistol receiver extension (end of the extension) is considered a pistol. Add a VFG to pistol, it becomes an AOW, and needs a tax stamp. 10.5" barrels would have to be P&W'd with a longer flash hider/device or flash can, some/most 11.5" barrels would have to be P&W'd depending on the receiver extension and installed flash hider/suppressor to get over 26" OAL. 12+ inch barrels get you over the 26" OAL threshold to become firearm length but, again, needs to have a VFG to be a "firearm" or "other" firearm as they like to be called. Not a biggie if you live in a "pistol friendly state", then you can take the VFG on and off at will if you wish. I'm not a lawyer and this all depends on one's own state laws, and, how it is built with different barrel lengths, receiver extensions and flash hidders/devices/etc and if you want to P&W them or not.
I think, NJSP said one can build their own "firearm" but not recommended so not to possibly violate constructive intent laws. But I'm not a lawyer and live in a free state.
I built two firearms, one with a 12" barrel and one with a 12.5" barrel. They are fun and like them as I like quad rails and VFGs. The 12" barrel will stay as a firearm as I live close to and border a communist state, Illinois, where most SBRs (without jumping through hoops) and sound suppressors are not allowed or legal. The 12.5" is built as I wait to jump into the stamp game, then to get a short suppressor and SBR it to a 10.5" barrel.
This was a little long but just wanted to explain what they are and why some people would want to buy or build a firearm.
me