I have this lip on an e92 M3 dropped on H&R Sport Plus springs. I am not going to lie, but if you are using your car as a daily driver, you need to be very cautious of where you go. Your wheels are on the outside of the car, not the middle, therefore, the middle of the lip is susceptible to all things that can hit it from the middle of the car. Also need to be careful for humps in the roads, or approaching bridges that always have that small crack before the bridge raises. That is my experience. It will make contact with the ground every so often. My lip is literally 2 inches from tip to ground. So far, I have had good luck, but there are those occasional times where I have been faced with an obstacle of a higher pavement area and how to get around it without scratching the lip.
Separately, at high speeds, the car has some definite downforce because of the lip.
Previous: '04 BMW E46 ///M3
Current: '08 BMW E92 ///M3, Space Grey, 6MT