The plastic rails are there to help you assemble the pistols. They will wear a bit ,keep it cleaned and then will just stop wearing. Heck you can cut them back to clear if you wish. Look at the frame. The 2 metal pieces embedded at the back of the top rail area is what expect the slide run on but just control the rear of the slide. The 2 ss sheet metal pieces embedded down where the recoil sping runs and the 2 cuts in the front of the slide is the front control area. Yes that small knock should also be there. Lube it well and shoot the heck out of it.
If you could use some extra grip control for break in. Go by a bicicle shop and get a junk skinny bike inner tube. Cut several pieces, 1/2" wide 1" , 1/2" and 2". Place the them on the grip thin to large ,trim the last one. Gives you a bit of extra palm swell and grip, aids control if needed.
I have a cm9 and cw9. 2100 rounds total with no issues at all.