Read an article by GM that said after extensive wind tunnel tests that the following, in order, were the most efficient for gas mileage and lowest wind drag.
1. cover---like comes on some of our trucks.
2. open but WITH tail gate up.
3. no tail gate.
It stated that the tailgate up created an air bubble that made the wind flow over the cab, across the bubble and over the tail gate. Without the tailgate the bubble was removed and the wind came over the cab and circled back against the rear of the cab and caused a huge drag. Ergo, the tailgate down or the mesh tailgate that lets the air flow thru are a no no for better air drag.
Therefore I believe that your little piece on the top of the tailgate is useless----plus not attractive----at least to me. But I may be totally wrong, just can't see the value. May even be disruptive to the proper air flow.