Will this diffuser hang lower than the stock bumper?

Grid-style diffusers are typically designed to align with or sit slightly below the OEM bumper line. Check your vehicle's ride height and driveway incline angle before installation — if you frequently encounter steep angles or low clearance areas, verify fitment with your specific setup.

Is this purely cosmetic or does it serve a functional purpose?

This is a cosmetic diffuser. It enhances the visual profile of the rear end through grid detailing and depth. It does not generate aerodynamic downforce or alter airflow.

What should I do before painting this diffuser?

Sand and prep the surface thoroughly before applying your chosen finish. The raw FRP condition means the FRP is sealed and ready to accept paint — follow your paint supplier's surface prep recommendations for best adhesion and durability.