Not sure if serious
On the one hand, you’re not forking out the NFA tax. On the other, is that really how you’d want to fire an AR? On the third hand, you have an AR-15.
Update: To be clear given my tendency to leave out whole sentences, this is a prosthetic device for those without the use of an arm. But I’m thinking of its application otherwise, which I would think would be the majority of folks who would get one.