The point of a brace is to stabilize the forearm. If that is the intent and it does that, fine. One of the important considerations having read the threads here with the posted info direct from the ATF is they see any flat vertical surface on the rear of the brace as capable of being a shoulder stock. That leads to the SIG and Shockwave only being as thick as the edge of the material formed. They look all cool in profile for marketing purposes, from the shoulder view there's not much to go on. One or two thin cross sections of polymer.
That goes along with one members attempt to stack a rail mount fore end hand stop under the tube, which made for a vestigal shoulder stock and the ATF called him out on it in the response. No, you can't have a flat vertical surface - the one important feature.
If the cheek pieces we see had more surface area over the buffer tube in a flat vertically oriented plane they wouldn't likely be approved, either. Cutting down an MFT Minimalist might get you by - without a letter of approval the ATF does seem to consider you guilty until a judge says you aren't. That's called enforcement from their point of view.
There is a simple buffer tube stock plate that is basically a wire loop, it's called a shoulder stock, so the idea of using an enlarged sling loop probably won't work either.
Goes to the point, tho - pistols don't have stocks. In 5.56, an AR pistol doesnt have significant recoil, they can be fired holding the stock against the chin and that was the most common way in Basic Training to demonstrate the LACK of recoil. For the most part a rear stock on the weapon only stabilizes the back sight - and since the gun is mostly intended to shoot at targets under 100m, it's not a major issue. It's a 2 MOA gun being aimed at 18 MOA targets, whether deer hunting or silhouettes. Stabilize it against your cheek or nose, it's not going to knock you down and injure you.
I shoot mine nose to the charging handle with the sling over my off shoulder pulling FORWARD. Tensioned I get it pretty tight just to reach my nose. I don't shoot squared up, I shoot from a side stance to brace the off arm against the chest. It's stable enough.
All the internet interest in getting a fake legal stock on the AR pistol is really an excuse to sidestep going out and learning how to shoot it better by practicing. That takes work.