The custom PHP FICM programming takes all of the best things from all of the various FORD OEM programming strategies, rolls them together, and then adds in its own secret sauce to provide better drivability and the possibility of better fuel economy. On an 05 Excursion, we noted gains of about 2.5mpg in mixed highway/driving and much decreased turbo spool-up times with the 'Atlas 40' tune on top of the SCT 'street tune' that was already loaded. With the tune in place, when the light turns green, you go and go almost immediately now. The truck drives more like a gas truck than a diesel. Crazy spool-up times are a thing of the past!
Of course, everyone drives their truck differently. About 4 of 5 are noting better fuel economy numbers (2-3mpg seems to be the norm) regardless of which tune they elect (fuel economy benefits are the same regardless of tune selected), but nearly everyone tips their hat to the better drivability.
Given the same driving style, there won't be any real differences in fuel economy between the various tunes - the power tunes (Atlas 40, Atlas 80, and Hercules) just provide some extra ponies with the option of the better fuel economy and that decreased turbo lag that you get from the Eco tune alone. Some have seen a VERY slight mileage gain from the Atlas 40 over the Eco tune.
Note that those experiencing the highest mileage gains are coming from the latest version of Ford's software. Those using earlier software strategies report mixed results. While most still report some gain, perhaps 1 in 10 indicate no mileage gain at all.