Will this diffuser scrape on steep driveways or inclines?

The Boss profile sits at the rear bumper line with minimal extension. Most driveways won't cause contact, but verify clearance on your own driveway by checking the angle of approach at the rear bumper. High-speed ramps or aggressive speed bumps are where rear diffusers typically see risk.

Is this diffuser functional or cosmetic?

This is a styling piece that follows Boss design language. It's not engineered to generate downforce or alter airflow. It works as a visual accent that complements the rear bumper aesthetic.

What prep should I do before paint?

Sand and prep the surface thoroughly before applying your chosen finish. Since it ships raw FRP, a light scuff with fine-grit sandpaper followed by primer and topcoat will ensure proper adhesion and a factory-matched result.