Coming from the Class III community, I would never even want to be around one. As TR pointed out it draws some serious unwanted attention. If you have a Registered Machine Gun, you at least have all your “papers” to show the curious or pissed off LEO. This stock reminds me of the Akins accelerator for the 10/22 which was at one time legal, with a BATFE letter, and then overnight the ATF made them all illegal and you had to either send them your springs, or destroy it. So yes, it is a “technical loophole”, however, it is whatever the BATFE says it is and that can change with the drop of a hat. People have been prosecuted for less.
Article on Akins Accelerator: Full of anti-gun rants...
http://beta2.tbo.com/business/consum...uin-ar-176333/
Youtube Video:
http://www.youtube.com/watch?v=9P8AbTKvykE