I have a Comp M3 and the rubber shield slips on AFTER the unit is mounted. Without the shield, the M3 looks just like the M2.
I don't use the rubber shield on my unit because it's too "baggy"
; it's made to fit scope mounts that have the bolt flanges at the top or the sides, so if your bolt flanges are on the sides, then there's an empty rubber pocket on the top, or vice versa.