“Will not comply” doesn’t bother the AFT a bit. Tons of people didn’t and don’t comply with the NFA. They don’t bother chasing everyone down with an illegal machine gun or who has taped a soda bottle to their .22. If not defeated in court (which seems unbelievable in the era of Bruen) - by someone who does the civil disobedience thing instead of the “do not comply” thing - it will just be another add-on charge they hit people with who are having their weapons seized for something else, or something used by snitches to justify their sweetheart plea deals.
For the AFT, lawbreakers are their customers. In some cases more literally, in others more figuratively.
All I can say is that if you do get busted for your illegal arm brace, don’t take the plea deal they offer. This will only be fixed by the courts when someone risks serious jail time in a trial. If you don’t get busted, find someone who is serving as a test case and fund their defense.