I have one and it works as advertised on a 5.56mm S&W M&P-15. Several people have tried mine and we are all able to fire at the apparent cyclic rate of an M-16.
However I have seen some internet videos of people who have apparently made the Slide Fire work on 9mm and .22 LR AR's and I have not been able to duplicate their success with my Colt 9mm AR or S&W M&P-15/22.
So they work as advertised on 5.56's but can be less successful on smaller calibers.
