Q: Is this a real diffuser or a cover that sticks over the stock one?

It is a full replacement rear diffuser, not a stick-on cover. It swaps out the OEM lower rear fascia entirely and includes carbon hitch and tow hook covers so you keep towing and track functionality. That is a meaningful difference from cosmetic diffuser wraps: this piece replaces the factory part and carries the design into a more aggressive, track-focused shape while keeping the Model Y’s rear lines. It is also one of the three pieces in the 2020-2025 carbon aero package if you want the matched front-to-rear set.