Will this diffuser scrape on driveway inclines or speed bumps?

Diffuser depth depends on your vehicle's stock rear overhang and suspension ride height. Measure your current ground clearance at the bumper before installing. If you've lowered the vehicle, verify clearance on your typical driving routes — this diffuser adds extension to the rear end.

Is this diffuser functional or cosmetic?

This is a styling component. The Super Fin profile mimics functional diffuser aesthetics and can help manage underbody airflow, but it's designed primarily for visual impact. If you're looking for measurable aerodynamic tuning, consult your vehicle's performance documentation.

What prep work is needed before paint?

Sand the surface to 220-grit or higher and clean thoroughly with a wax and grease remover before applying basecoat. FRP can accept most automotive paint systems — follow your paint supplier's guidelines for adhesion and cure times on plastic substrates.