Will this diffuser scrape on driveway inclines or speed bumps?

Verify ground clearance by measuring the distance from your factory rear bumper to the ground on an incline. The Zamba profile extends beyond the stock bumper line, so factor that additional reach into your clearance check before final installation.

Does the Zamba diffuser provide functional downforce or is it cosmetic?

This is a styling piece designed to enhance the visual profile of the rear end. For aerodynamic benefit, you'd need an integrated rear wing or full aero package working in concert with this diffuser.

What prep work should I do before painting or coating this?

Sand and prep the surface according to your chosen finish system—whether that's urethane paint, vinyl wrap, or powder coat. Your paint supplier will recommend grit and surface conditioning based on what you're applying.