As fun as this looks, it is only a matter of time before the ATF wises up and bans it down south.
The concept of a stock for bump fire is not new. The last guy that tried to market one (Google "Akins Accelerator 10/22") had a patented and BATF approved device on the market for TWO years before the ATF wised up and banned them. They knocked on the door of every customer to retrieve them all too.
I expect this product will end up like Akins
http://www2.tbo.com/content/2007/dec/18/211606/pasco-marksmans-invention-leads-him-ruin/
"They were selling like hotcakes," Akins said. "We were truly amazed by the response."
That was until the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives banned the Accelerator — two years after approving it.
To the ATF, the mechanism is an illegal converter kit that, if it fell into the wrong hands, could turn a run-of the-mill target rifle into a 700-round-per-minute killing machine.
Under the threat of imprisonment, officials ordered Akins to cease production, turn over the recoil springs from his existing stock and hand over his customer list.
And they didn't give him a dime in return."
For a funny bump firing read, Google "ATF Machinegun shoelace". The ATF declared in court that a simple 14" looped shoelace was a machine gun.