According to SB tactical, ATF announced clarification of the shouldering interpretation that was made in 2015.
SB Tactical makes the SIG Arm Brace and the letter covers what SB Tactical makes. At this point, it doesn't cover other companys' similar product.
Military Arms Channel discusses the issue
And you can read more from The Firearm Blog
http://www.thefirearmblog.com/blog/2017/04/24/breaking-news-update-atf-reversal-letter-sb-tactical/
From: Military Arms Channel, The Firearm Blog
