No one who set out to design a pistol brace ever created anything that couldn't be considered to be a field-expedient/somewhat sub-par stock, either. Frankly, the whole thing is ridiculous - AR and AK "pistols" fire rifle cartridges from rifle-sized guns which happen to have shorter than average barrels. The idea that these guns are not rifles purely because they sometimes lack a full/proper stock is fairly silly. Even before braces became a big thing, AR and AK "pistols" existed almost purely to blow a raspberry at the NFA, and the ones that didn't exist for that purpose existed to blow a raspberry at handgun-only hunting seasons and handgun/shotgun only zones for deer and other large game.