IMO, air flow loss for cooling the brakes that could be affected by these shields is negligible. Id leave them on personally for cleanliness. There is abundant flow behind the wheel under the car if you are worried about it, but think about what you guys are saying,

I doubt the brakes really require a certain amount of air flow over them for cooling properly, they should work just as well with now air flow as with tons.
Heavy truck dually brake setups are almost completely covered by solid steel wheels, where adequate braking and heat shedding is a far more important consideration, yet there are often no or few holes in the wheel itself. If proper braking heat loss really depended on outside the wheel air flow, these cars would all have been designed with very special air scooping rims, not bundts and steels.
We are worrying about a non issue here.

MB Steel wheels and hubcaps are almost a solid surface also, but we're not worried about those

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