I have a LMT standard patrol rifle (M4) w/ the standard oval hand guard. I have mounted my optics, Trijicon NSN Reflex on the upper receiver. Im considering buying a rail system handguard for it. Ive seen Knights Armament USGI sets (w/ covers & handle) for less than $200 on eBay. I do not want to remove and replace my front sight housing. Are there any real quality differences in available rail systems? Is there one I should be looking at? There seems to be quite a few options available for our M4 type rifles.