It remaps the ECU to offer both a fuel efficient mode and a sport mode controlled by the cruise control switch. But for the auto it also changes shift points and in Eco mode, shifts into higher gears much sooner for better fuel economy.
From the dealer I ordered from, it was said to be non-refundable since its locked to your VIN. And with the transparency mode there are a number that say they've gone to the dealership with it and it didn't show up on a scan.
Xtreme you also have the stick. That was with the automatic. The gains with the stick probably are far less. I will report back in 2 weeks on my fuel economy with the Eco mode tune on my car. Since thats about how long a tank lasts. So far according to the DIC its already reading higher on the average with the same driving style. I will say when driving though and looking at the instant mpg reading, it almost seems to read lower though. So I'll just have to wait and see when I fill up.