That depends on the quality of the FFL. Just on the Shockwave and TAC14 alone, I’ve had conversations with local FFLs...three FFLs, two different opinions of legal configurations regarding arm braces. One of the FFLs is so misguided he would gladly transfer you an illegal gun and think nothing of it...a 14.5 AR upper that’s “permanently” attached with rock-set was something he mentioned as legal.
Anecdotally, I’ve seen a 17.5” shotgun for sale at gun shop, a Glock 17 for sale...with a shoulder stock attached in the display case, and my all time favorite, a 1940s Winchester 94 cut down to 14” being sold as a factory model exempt from NFA. Getting those from an FFL doesn’t make them legal.
If you get it from an FFL, you *might* have an argument to make with the DA, but ignorance is not a valid defense...for you or the FFL.
As for a Shockwave in NY, it doesn’t seem definitive to me and it would depend on my legal research, my locality law enforcement and how badly I wanted a novelty item that fires shot shells.