just wanted to chime in a bit as I found out about the needed changes to fit the diffuser AFTER I ordered it.
I have a thread in the exhaust section all about it. But essentially the top of the diffuser is a direct fit and will clip right into the bumper. However, once you remove your stock one you'll notice whats called the adapter plate which also contains all the PDC sensor modules and etc. It is NOT a fit with the M5 diffuser as it is wider than the diffuser will allow. I suppose at some point you could order the OEM M5 part but as of a month ago when I did mine it was not available. So the alternative is trimming the plastic adapter plate down by quite a bit and either working around the sensors or moving them slightly (I did the latter). You will also need to have your exhaust shop work with the exhaust to move it roughly 1-2" inward on each side as the openings are different for the M5. So essentially its a non-direct....direct fit. lmao. But all this being said as long as you're ok with some minor cutting which no one will ever see anyway, then its still a pretty simple upgrade. Just don't expect it to be completely plug and play. Also, be sure to use a reputable shop as always.
Happy Modding...PM me if you need any more help