Will this diffuser scrape on steep inclines or speed bumps?

The two-piece design sits close to the factory bumper line, so clearance depends on your vehicle's suspension height and driving style. Measure the gap between your current rear bumper and the ground, then compare it against the diffuser's profile before installation. If you run lowered suspension, test clearance at your typical approach angles before committing to fasteners.

Is this purely cosmetic or does it add downforce?

A rear diffuser in this configuration is primarily styling-focused. It complements the rear bumper aesthetic and creates visual aggression in the Mystic profile. For measurable aerodynamic benefit, you'd need a much larger, track-oriented diffuser with ducting underneath — this is not that part.

What prep work do I need before installation?

Sand and prep the mounting surface on your rear bumper to ensure proper adhesion if using epoxy or adhesive fastening. If using mechanical fasteners (bolts or rivets), mark your hole locations carefully against the bumper's geometry. Inspect the diffuser for any surface damage in shipping and verify fit against your bumper before final fastening.