Will the diffuser scrape on inclines or driveways?

The diffuser extends minimally below the stock bumper line. Verify ground clearance on your vehicle's current suspension setup before installation. If you've lowered the car significantly, test fitment at a slight angle first.

Is this diffuser functional downforce or purely cosmetic?

This is a styling piece designed to enhance the aggressive look of the rear bumper. It's not engineered for aerodynamic load. Pair it with your existing suspension and braking setup.

What prep work does the FRP need before painting?

Sand the surface to accept your primer and paint system. The panel arrives in raw FRP condition, meaning it's been gel-coated and prepped for topcoat application. Follow your paint manufacturer's surface prep guidelines for best adhesion.