I had the Edge Juice installed for almost 2 years now until I starting having problems and sent it back to Edge for diagnostics (still awaiting response from Edge). After removing the Edge my mileage went up from about 16. 5 to just over 20mpg (using Level #1). I drive around town, work, stores, etc. on Level #1 which is Edge's MILEAGE setting. When towing I set it to Level #2 TOW. While towing ~12k# flat gooseneck trailer I got 10. 5mpg... . the worst mileage I ever got towing with Edge set to TOW. Can't imagine what driving around on the EXTREME setting would give you!!!
Now, in Edge's defense, the power is awesome! Truck was dynoed at 778 ft-lbs at the wheels on Level 5. But you can't tow with #5, and shouldn't or really can't drive around on level #5 so why bother to have it???? I find myself doing 95% of my driving on level #1 MILEAGE, 4% on TOW and maybe the other 1% or so on Level #5 when showing off. With diesel hovering at $2. 50/gallon, and for such little time I use Level #5 I can't justify keeping it when it gets sent back to me.
So... bottomline..... I'd stay away from Edge if you are looking for mileage!!!