I have one. My feed ramps appear to be the standard type, the receiver definitely doesn't have the m4 cuts.
I use a standard carbine buffer. No heavy markings on it.
The fsb that came with mine is f marked. It was sold to me as a complete rra upper in this configuration. Upper is laser infrared rra on the top rail.
Never had any feeding issues whatsoever with this one but I've never ran junk ammo thought it either. Always federal, winchester or AE xm193 or winchester 64 grain soft point ammo.
Accuracy is sufficient. Never sat down to see what groups it's really capable of. No need to really, for its purpose as a short carbine it gets the job more than done.
mine was awfully heavy. Then I removed my kx3.
. It is still got a bit of weight with the rail,light and vfg attached.