Extremely late to the party.
I have never ventured into the world of braces, SBRs, AOWs, machine guns, suppressors because of a lack of time/talent/treasure to acquire and/or navigate the legalities.
IIRC, when I worked in an office from 98 to the sunset of the AWB in 2004, there were zero freestanding AWB cases charged in a district that was a perineal top 5 office terms of prosecutions re firearms offenses ( mostly Felons with a smattering of drug users, aliens etc.)
In my district/region -The regulation side of ATF is busy enough keeping honest people honest. The enforcement side is busy enough bringing cases against violent folks and other worthy targets on a regular basis.
I am sure there have been a few outliers-somewhere. I am sure those outliers did/can/will and should, to the extent applicable where legally supportable under theirs facts/circumstances, avail themselves of any and all legal remedies.