I bought a CF diffuser from Taiwan. The removal of the old diffuser is easy - just remove four (I think, from memory) snap bolts, which are plastic, and then working from one side to the other, work the tabs out of the lip on the bumper. Installation is similarly easy - fasten one side with the snap on bolts (which you can buy piecemeal from Mercedes parts), then work the tabs into the bumper lip, then fasten the other side.
The real problem is the quality of the CF diffusers. I returned mine because it was missing the tabs that go into the bumper lip (just had slots, no tabs to hold it) and was completely missing one bolt hole. Because the CF is MUCH less flexible than the plastic stock diffuser, it is really really hard to install without those tabs to hold it as you are forming around the bumper.
I had a terrible time trying to send it back (post office wouldn't take it and freight cost more than the diffuser) - but eBay finally stepped in and refunded my money.