Will this scrape on steep driveways or inclines?

The diffuser extends minimally from the bumper line. Check your approach angle before installation — if your factory bumper already scrapes on inclines, this panel will too. Test your current bumper clearance on your steepest entry to predict fitment.

Does the diffuser provide any functional downforce, or is it purely cosmetic?

This is a styling diffuser that mimics the look of performance aerodynamics. For measurable downforce at highway speeds, you'd need a much larger, engineered rear wing or splitter. Use this for the aesthetic — it won't change your car's handling.

What prep work should I do before painting?

Sand the surface with appropriate grit to scuff the finish, then wipe clean of dust. Apply your chosen primer and topcoat per the paint manufacturer's instructions. Proper surface prep before primer ensures a durable, professional finish.