Got my fast stock... for those on the fence, some observations:
Sling mounting officially sucks, but I kind of knew that - like stevo said, there is a QD swivel attachment at the bottom of the adapter and a SMALL hole on the side. I'm worried that trying to run a swivel on the bottom will cause the rifle to be unable to be slung in the "patrol" position comfortably because the sling won't be attached on the side. (try slinging a traditional hunting rifle in this manner to see what I am talking about) WTF Rob arms? it would have just as easy to put the QD hole on the side of the stock and have it ambidextrous.
The folding mechanism is a little shaky when in the regular "shooting position" - duct tape firmed it up. Going to try backing one of the two screws that holds the stock to the mechanism (for changing mounting height) out so it "bumps" against the receiver or adding a third.
For the mall ninjas that want to shoot with it folded, I hope you are a lefty. It's very difficult to hold with your right and work the trigger with it folded.
No real weight gain, balances the gun better IMHO.
The stock is a solid option, these are just my observations, YMMV for what you want it to do, but for now, the stock remains on my rifle...(until I find a ACR stock w/adapter)