A friend sent me the following on it and it appears to disagree that the decision only applies to the SB products:
I copied this from thefirearmblog's website, the formatting is all screwed up but on my computer at least it's legible, so hopefully you can read it as well. I also read the actual ATF letter and, the way it's worded, I'm pretty confident that the guy I'm quoting below is correct: it's not just the Sig brace, but any brace as long as it isn't set up in a way that would make it impractical to still use as an arm brace and/or is permanently attached to the rifle.
Nicholas C, since you bring up the Shockwave Blade at the end of your article--and that you don't know its current status, I will let you in on what I learned today:
I just got off the phone with a very nice gentleman at ATF Tech Branch---who was fielding these calls today. (He was, understandably, very well versed on the subject---and very nice about it even though he's been on the phone all day, repeating himself ad nauseam.) I identified myself and asked him specifically if the letter that's making the rounds is limited to one company's products--or if it applies to all pistol stabilizing braces. He said: "The letter covers all pistol stabilizing braces, including the Shockwave Blade." So that settles that.
He then gave me two points of further guidance for our customers:
1. By "permanent affixing," ATF considers that to be adding permanent Loctite to the large set screw that secures the Blade into the dimples in the KAK tube. As long as you don't red Loctite the set screw in place, ATF considers it to be "temporarily placed" and "perfectly okay to shoulder." (He didn't beat around the bush on this topic.)
2. "Length of pull"---for lack of a better word regarding pistol braces---begins to enter a "gray area" above 13.5". Above 13.5" begins "to enter shoulder stock area." (His words. I believe this has to do with the "comfortableness" aspect.) On an AR-15 pistol, the "length of pull" for the Blade is approximately 13.13", so no issues there. But if you use the Blade on a firearm that requires a large adapter of some sort, please make sure that you only use the dimples up to the point that you remain below the 13.5" length. Stay below 13.5" and according to ATF, it's okay to shoulder a Shockwave Blade.
So there you have it. Anything you read to the contrary on a web forum, social media site, or industry blog is simple misinformation.
Per:
https://disqus.com/by/martyewer/
Personally I don't know who Marty Yewer is or if he is a reliable source of info but if what he says is correct then it seems to apply to pretty much all the brands.