My opinion, based on as-controlled-as-possible A-B-A testing (straight & level road, absent any other traffic, cruise controlled, back to back bi-directional runs) is you'll not likely see any drag reduction using AirTabs. Seen this?
http://ecomodder.com/forum/showthrea...olla-2390.html
It's fairly well known that some rear spoilers reduce drag (and rear lift).
They are typically added to most sedan/notchback hybrids (and other high efficiency versions of that body style), where the "regular" edition may have none.
Honda Canada added a small deck lid spoiler to its non-hybrid sedan/coupe as one of a series of measures meant to marginally reduce the car's fuel consumption to make it eligible for federal incentives.
Car and Driver measured drag reduction on both its "Crisis Fighter" ecomodding project cars years ago (See the
Pinto project here). Their Datsun 240 project also benefitted (through reduced fuel consumption) from a spoiler addition.