If its legal, great. I'd just rather someone else do the beta testing on that issue. Honestly though, if I could get a FA AR I couldn't afford to feed it. FQ13
Its a variation of the ole "bump" firing .
In a nutshell, FQ, to answer your question on legality: It is legal under 'current' standards because the actuator is controlled by the shooter and is not a component of the internal working mechanism of the trigger group. The internal trigger control is not affected like it would be with a sear disconnect altering mechanism. This unit seems to control the rate of fire based on external manipulation of the trigger. It appears to use the recoil inertia of the rifle to press the trigger faster than the shooter would normally be able to do with just a finger. In the video note the stock sliding back and forth with recoil as the trigger finger rests against the sliding unit. (this is all just supposition based on what I saw in the video).
Even though it doesn't effect the internal firing mechanism it can still be considered illegal. There have been people that have gotten nailed by ATF for "shoe string machine guns." Basically they took their shoe stirngs and tied them just right to the triger, so that the string would strech just far enough forward for the sear to reset before it would snap back and trip the sear again.
Someone made a spring loaded stock for the 10/22 that worked the same way. ATF approved it then outlawed it. I expect the same thing here.
They also market that windup thingy on the trigger, turn it and the trigger goes back and forth. But this is really the best Ive seen. If its legal, I may buy another poodle shooter, just for in case I need it.