Not bad but lacks attention to detail
I purchased the Q50 carbon fiber splitter based on the measurements for a custom install on my 2012 M37. The fitment and customization wasn't a problem; it looks pretty good with the shape and dimensions but I have some criticism with the splitter itself.
First off, if you split it down the middle the two halves are not a mirror image. I measured 100 times from every conceivable angle and direction and it's always off by an inch or more. It took a lot of extra time and alignment to my bumper to get it "close enough" to even on both sides so as not to be obviously sticking out more on one side than the other.
Second, it's thin. It looks thick in the pics because the lip rolls over but it's hollow and thin. I already have a chip in the front edge from a rock or something popping up. Also with the edge being hollow, when I had to trim some off the back edge of the splitter; it's now an open edge on the back side and looks unfinished.
Third, it doesn't come with any clear coat so be prepared for the extra cost of taking it to a shop to have it sprayed.
Overall it looks decent but it lacks that finished refinement for a proper 5 star review.