Many people like flat flares for the clearance they provide. Others like the way they look. We had flat flares on the TrailRunner JK for tire clearance. They provided the clearance, but didn't work in the wet, in the mud, etc. The mud flew up and back onto the hood and windshield until I couldn't see out of the Jeep.
I've decided to go back to 35" tires for less unsprung weight. With 35s, the OE flares work. I had saved the original flares from TrailRunner and figured it would be easy to pop them back on. Ha. John Williams at Impulse Offroad helped and it wasn't easy to install the flares, the support brackets, and the inner fender liners while dealing with the nutserts that had been installed for the flat flares.
We were succesful, though. The flares are mounted better than ever as we were able to utilize some of the nutserts instead of relying on the OE plastic clips.