Much to my surprise, an Anderson complete mil-spec FCG that came installed in an FMK AR polymer lower permitted bi-directional fire and sometimes second round fire on trigger reset. I called the out of State vendor who advised me that they were aware of the problem !  Not sure if they became aware before or after I purchased the complete lower for a lightweight AR build.  So I have returned the complete lower to them for FCG replacement. Accordingly, if you are purchasing an FMK  complete lower where the vendor has installed Anderson components or if you are purchasing from Anderson, be careful. 

I'm more interested in, was it reliable binary fire?  If so I woulda kept that sucker as-is and secretly analysed the shit out of it.

No it was not reliable binary fire but intermittent. It was kind of fun to shoot it that way, but it had to go back for obvious reasons