Airtabs on my Super C have worker great. 
Fuel mileage improvement. I cannot tell. 
Cross winds improvement. Has created a better handling MH.
Clean back of MH and toad. Not much better. It is still dirty when I get to a new destination and it has rained.
Biggest improvement was installing AirTab on the cab over just above windshield. Stop bugs from being plastered to  bottom of overhang. Also stopped noise at cab side windows by changing direction of air flow.
This will not help a Class A. But it sure helps Class C and TC's.