[Lazamataz]

Idiocy aside, I note that the ruling says “When attached to a firearm”.

So, it is legal when not attached.

This is more of that idiotic stuff, like the ATF claiming that a wrist-brace for a pistol AR is legal, but the second you SHOULDER it, it becomes an SBR.

[SVTCobra03]

YES, It Is Legal to Shoulder an AR-15 Pistol Equipped with an Arm Brace

https://www.thetruthaboutguns.com/2017/04/foghorn/atf-its-legal-to-shoulder-an-ar-15-pistol-equipped-with-an-sb-tactical-arm-brace/