I went back over and had a gander at the "brace" again today. Made sure to have a tape measure handy. Minimum length of pull is 7.5" from where the sling bracket is placed behind the receiver to the back of the buttstock. Here's what I didn't realize; The stock, er, brace, is adjustable. You can twist it back on the buffer tube as far as you like, though it takes a little doing. I didn't realize that was possible until my buddy demonstrated. I thought it was hard mounted.
You can adjust length of pull, or rather how far the brace will go back on your forearm, to the point where it can suit any user as a full functional buttstock. If you usually run on the third notch back on your six position adjustable you can also set this to give you the same length of pull.
As far as buttstock function, it is as good as a six position. Only drawback is the comb near the receiver side of the brace is flattened to allow for the charging handle to pull back with the stock all the way forward so it leaves a slight corner that goes into your cheek. Considering the minimal recoil from an 5.56 weapon it's no big deal just not quite as comfy as your standard six position fully shouldered. But hey, at least it don't go rattle rattle. Outside of that small caveat it works as good as your standard buttstock.
If Sam is right about not having to worry about the legal status then this item is a game changer because it allows anyone to have an SBR without the hassle and wait of NFA paperwork because it works as well as any basic six position stock I've tried.