I decided to try out some
M style mirror caps from Aliexpress and I wanted to share my thoughts. At $84 shipped, it was such a great deal, I couldn't pass up on giving them a shot. I got them in black, but they also have them in a carbon fiber look. I placed the order on Feb 4 and received it on Mar 14, which is quite awhile. Obviously because they're coming from China, that could be a factor for anyone who doesn't want to wait.
Fitment seems perfect. In fact, I have a hard time imagining them being any better. The color matches the black trim perfectly.
Overall, it's only been a couple weeks but I'm really happy with them. They're sportier than the OEM style which may not be your cup of tea but obviously, the black is far better than the cerium gray especially on my glacier silver X4. As long as the color doesn't fade I imagine these are a great option for anyone who doesn't want to pay $340 for painted ones from IND and you like the look of the M style caps.
The car is dirty, but you get the idea.