I think what you most want to worry about is the paint.
Matching your aprons/skirts to the same body color of your other part of the car is a challenge. I have heard many complaint from car owner on paint body shops that they are unable to match, mix match colors. Especially if your car is not brand new (few months old)
I bought mine (M Tech) from BMWHK; they are more expensive than what was available online, but I admit, they paint job they did is great. nothing to complain about...