[mockngbrd]

I can help to chip in here for a part of the reason for these "M Performance" parts.

Similarly, I was also wondering why would BMW bother offering such bits when the aftermarket scene offers so much more.

So from my conversations with a German friend, it's all to do with TUV homologation and engineering approval. Because getting such certification is a very time-consuming and $$$-intensive process, not many smaller tuners are willing to get their parts homologated for Germany which means there are not as many aftermarket parts for cars as the rest of the world gets. An example he mentioned was to go look at BBS's wheel catalogue for Germany vs the rest of the World. Because each homologation process is tied to a specific car model (eg: E90) + its specific model level (E90 + 335i).

Meaning, you cannot legally use a BBS wheel that has been homologated on an E90 335i on an E90 328i if it has not been homologated also for the 328i. And yes, you can be stopped on the road by the police for such infringements. Or that was what I was told, so I could be wrong.

This is also why you see German tuners (ACS/Hartge/etc etc) offering "fully" tuned cars, cos they need to homologate almost every single thing. And why their parts also cost so much $$$.

And so to allow an easy way of customising their cars without any TUV hassle, BMW offers these "tuner" parts from the factory direct. You don't have to slap them on, but they offer it as an easy way to customise your car when ordering it.

Also a reason why there are so many "spec/trim" levels for a single model.