since FN made tons of M16A2 rifles for the armed forces I am sure that there will be no QC issues. I was issued three different M16A2's during my years in, all were FN.
I did not even know that you could do the C-Clamp grip on a completely unmodified A2 handguard. I thought that you had to have at least one Magpul furniture item to make it work.