The courts have already shot this down. Enjoy your pistol brace.
The problem will be if you get the wrong agent, then you are in court fighting for your freedom. It's still going to cost you lawyers fees, time off work, etc.
What if you wanted to sell a gun with a pistol brace? The ATF gets wind of it, decides they will purchase from you, you not knowing, and off the federal slammer you go, until a lawyer gets you out and a pile of money is spent.
I agree, the courts have shot it down, the ATF isn't giving up, they are still looking for ways around the court.
These liberals aren't going down without fights, just look at the pardons for Jan.6ers, and the wardon not following the order. They still stayed in prison.