Will this diffuser sit flush with the rear bumper, or will it stick out?

The AF-1 profile is engineered to mount into the factory diffuser cavity without extension beyond the bumper line. Verify that your vehicle has the AMG sport bumper before ordering — the mounting points differ on non-AMG models.

Is this diffuser functional or cosmetic?

The AF-1 is a purpose-built aerodynamic design. While it produces downforce at highway speeds, the primary benefit is the refined appearance and significant weight reduction compared to the factory plastic diffuser.

What finish should I apply to the carbon fiber?

Carbon fiber is delivered unfinished. A clear coat is recommended to protect the weave from UV exposure and road contaminants. Sand and prep the surface before applying your chosen finish to ensure proper adhesion.