Of braces and Honey Badgers
So, as a backgrounder, the Honey Badger, the gun that broke the internet in 2012 came originally from Georgia-based AAC, the byproduct of a proposed replacement for the HK MP5/MP7 for use by special operations groups.
Thus: The circa 2012 O.G. AAC Honey Badger, which was proposed as the Low Visibility Carbine for special ops about a decade ago, upping the ante on the MP5/MP7 with .300 Blackout. Of interest, I held this very gatt in Remington’s Gun Library in Hunstville a few years ago.
Kevin Brittingham, whose team at AAC developed the Honey Badger initially, moved on and started Q in New Hampshire in 2017, with the current version of the HBP as its flagship firearm. Q, up until very recently, sold it both as an SBR which required a tax stamp, and as a no-stamp-required pistol using an SB Tactical stabilizing arm brace.
Boom: the current Q Honey Badger Pistol. No select-fire and an arm brace sans stock.
A possible reason could be that Q formerly listed the HB Pistol version as having a “2-POSITION TELESCOPING STOCK” rather than a brace on their website once upon a time, which seems just like a copy/paste mistake when their e-comm person set up the page, using the same copy from the SBR page.
But, the minor mistake in advertising, which surely could be easily cleared up, has now gone nuclear and the ATF isn’t taking any prisoners in the effort to dub the HBP an SBR through some sort of arbitrary concept without showing their mental gymnastics. The end result could be upwards of 4 million legal gun owners who have braces on their AR/AK pistols becoming potential felons by default once the smoke clears.
laststandonzombieisland 
So, if those 4 million owners were to put up $100 each, they’d have an $400M war chest to take BATFE and the Federal government to court with.
Pretty sure that’s enough to cause some trouble. And a few million people probably count towards “common usage”.