Its not at all difficult to remove the OE diffuser, there are several screws along the bottom, and the clips come out with modest force. Just be careful about how you pull on the clips, the bumper flexes with it. Take your time and its simple. There are multiple high quality cf diffusers out there.
E88 FBO N54 Alpinweiss/Coral Red/RB Turbos/Meisterschaft Race/Berk Resonated/Macht Schnell 3"/ER CP/Synapse/VRSF FMIC/FFTEC LPFP/HFS-4 DO Stainless Lines/BMS DCI/BMS Thermostat Delete/Rob Beck PCV Valve + Cap/BMS OCC/PTF E50/ST Coilovers/M3 FCA + Tension Rods/M3 Subframe Bushings/M3 FSB/DINAN Camber Plates/Apex ARC-8/Project Kics/VAC Hubs/Rogue Transmission Mounts/Alpina TCU Flash/Icarbon/Kerscher/BMW Performance