No shouldering for me according to the BATF...
If you are using a Sig Brace then you are correct, BATFE clarified their findings on this design. However, there are SEVERAL other options out there that the BATFE has no issue with as they were not designed to "slip on your forearm" as the SIG was. People were misusing the SIG brace which forced the BATFE to clarify their findings.
The flaw was when Sig tried to skirt the rules by saying "oh, we wanted folks to put it on their forearm to help stabilize" instead of just designing a brace. The new "wave" of braces do not hide their intentions and the braces typically "slip" on and are only held on by friction.
And, one last thing, someone please correct me if I am wrong; I do not own a brace, never used one. Though I do question why I decided to get 2 lowers SBR'd now that the market has picked up and BATFE has indicated they have no issue with the current designs or purposes.