Bottom line, they're crap. There is no way some dongle placed on the rear, front, side, or bottom of a car is going to return any appreciable gain in aerodynamic efficiency. Keep in mind that the main cause of drag is form drag, or pressure drag on a road vehicle. This is only affected by changing the gross shape of the vehicle. Skin drag is pretty much insignificant and isn’t affected by these gas pods generating turbulence anyway since the air on a car is almost always turbulent to begin with. So you have a product claiming to do something that is already in place on a car. The air which is "Disturbed" by the passing of a vehicle extends out several feet in each direction, it isn't just the air 3 inches from the skin. If you don't believe me, then you haven't been paying attention to the grass and trees directly alongside a car or truck as it passes them.
This topic has been discussed with the owners of the company already.
GasPod Discussion on Ecomodder They stand behind their "Computer Simulation" results, but have no desire to do any real world ABA testing such as coast down or max speed down an incline. These tests would be easy as heck to do and the results fairly significant. I have a hunch they have done these tests, found no benefit, and know themselves they're selling a dream with no real science to back them up. All they have is anecdotal stories of people who use them and have X,Y or Z savings over time. Peoples stories are no way to prove a benefit due to the extremely variable nature of fuel efficiency from week to week, month to month, person to person of vehicles. Besides, whose going to buy these for $70-130 and come back and report they haven't done anygood?
They have a Facebook page too
GasPods on Facebook