The polymer rails are just for guiding the slide onto the frame in the assembly process. They could actually break off completely and it wouldn't hurt a thing. The slide only rides on the very front steel rails (one piece in the dust cover imbedded in the polymer) and the 2 steel segments in the rear. If you get any shaving of the polymer, it's only from the break-in/mating process. No worries.
Very solid design, actually. More rail surface than any of the G models.