Rapid Fire on it pretty much eliminates its entire purpose. Regular LSAT > Rapid Fire Mk48.
The LSAT has pretty much the same rate of fire for free, better iron sights, and less recoil. The Mk48 may have more damage and possibly more range (I don't know how much RF reduces it) but the added recoil makes it pretty moot. It's not all that hot at longer ranges with it on, and that's what the Mk48 is for.
If you want a LMG for closer ranges you should use one of the other three.
You are the universe Expressing itself as a human, for a little while
The target finder was a guilty joy for me, but I'd also try out the acog and eo tech. The reflex is meh since it doesn't offer zoom and the MK48 is meant to absolutely dominate longer ranges. The stock also helps since it's not pretty in cqc and abusing lag with it really helps.