Those might work. I don't know of anyone who has them. At first I thought you were talking about one of those big "jet blast" type deflectors that you sometimes see on the top of trucks and vans.
0.8 mpg increase might not be worth $200 for me.
2006 23B Hybrid with 10k round bar WDH
2011 F150 4x4 SCREW Ecoboost, Max Tow, Integrated TBC, 3.73 LS axle, Firestone Ride Rite airbags.