There was another thread on this recently. I think the only ones that were found with pics were on a 1 series. They actually didn't look too bad, but I doubt they were very functional.
I think your best bet is to just clear bra the areas susceptible to getting pelted with rocks and dirt from the road. In all honesty, I already have some damage there from rocks and will likely need to have it all repaired. You can't really tell since it's pretty low, but eventually it will get to a point where it'll need to be fixed. Once it does, I will clear bra it when it's all said and done.
'11 BMW E92 ///M3 - ZCP and DCT
'13 Toyota Tundra - 4x4 Platinum CrewMax, 5.7l iForce V8