A protective screen for the engine oil cooler on the S55-powered F8X cars: the F80 M3, the F82 and F83 M4, and the F87 M2 Competition. On these cars the cooler sits behind the lower bumper opening, unprotected, in the direct path of road debris.
A holed oil cooler on an S55 is one of the more common and more expensive things that happens to a car of this age, and it tends to happen on exactly the kind of drive people buy these cars for. The guard screens the core against gravel while still letting through the air the cooler needs.
It is a protective part rather than a performance one. No tune is required, no emissions equipment is affected, and it ships to all 50 states.