I just bought the Stillen Front Splitter and I removed the front bumper to install it. I removed the front bumper so I can install it with a screw and a nut inside the bumper. If you install it with the self tapping screws that came with the kit, after a while the lip will fly off. The shear wind and vibration will loosen the crappy screws and before you know it, you will not have a lip anymore. This method of install was recommended by at least 3 body shops that I went to. They were all quoting me about 200 for the install but I decided to do it myself and save me the $
Happy with the results