Does anyone have any experience with this adapter to allow AR stocks to fold to the side? If it’s ok to do, what options available for adapters that allow the brace to fold?
Yes, you can put a folding brace on an AR pistol. ATF has ruled that AR pistols with a certain type of brace do not meet the definition of a Short Barreled Rifle (SBR) and are therefore not subject to the NFA.
However, there are some important things to keep in mind. First, the pistol must not be fired from the shoulder. Second, the overall length of the pistol must be 26 inches or more with the brace extended.
Finally, the folding mechanism must not allow the brace to be extended without manually unfolding it first.