I have a KW T-300 with a 96" Bentz sleeper. I started putting Airtabs on my truck 2 years ago. My current count is 138.
When I put them on the roof and sides of the box as recommended, I found that big trucks don't suck anymore when they pass me.
I added them to the front of my sleeper, right where it levels out. That improved my fuel mileage by 3/10 of a mpg, because the air now flows over the top of the box.
They are on the top and side of my fenders. Last summer my truck consistently ran 20 degrees cooler than it had the last 2 years with no other changes.
They are on the back of my west-coast mirrors, the water doesn't wrap around like it used to. I've had too much else going on to be able to get mpg #s since adding those and the ones on the trailing edges of my toolboxes.
No, Lawrence, I don't like them, I just don't have any other use for my money