Magpul's original MOE, which they call Gen 1. has a flat top surface with 5 slots. Since the Gen 1 design is not piston compatible, Magpul changed the design of the Carbine, Mid & Rifle length MOE's to be piston compatible. The top surface is now peaked, with the Carbine having 4 top slots.
IWC's TMC (Top Mount Cantilever) Light Mounts attach to the Gen 1 5 slot-flat-top Carbine MOE.
IWC's SMC (Side Mount Cantilever) Light Mounts attach to tge slots on ALL and EVERY MOE Hand Guard.
They're the same price, with the same modularity and place the light in the same position.
Hope this helps!
+1 on QD mount and slot. I am going to get the kit that requires drilling the hole, but if I could do it again I would order the MP stock with it already installed.