As a maintenance manager for a major store chain supplier, I came across Airtabs as a way to improve fuel economy.
I can tell you, It works.
I installed the Airtabs on a Volvo tractor with the roof and side deflectors and with the same driver and same run from one year to the other was able to see a 2,7% improvement.
I also installed the Airtabs on a couple of trailers but was able to track the results.
I know the aerodynamics work.
They create a vortex (swirl) of air behind them making a wall that redirects the towards the rear instead of creating vaccumm in the open spaces.