The FN FS2k uses it and has proven reliable enough (which somehow they managed to make double the size of the RFB with the handling characteristics of a 4x4 post).
Really? I've run an F2000 and I found it to be very natural feeling. The only gripe I have is the safety - easy enough to reach but set up backwards if you ask me.
But, it is true, the RFB is silly small. I have no idea how the wizards at Kel-tec did that.