the cortex has a 2 year warranty for your vehicle with it so theres no reason NOT to get it. the flashpaq and cortex are the exact same except for the warranty.
the XS is just that. for better MPG's. since you have an 08 get the 3865(flashpaq) or the 3950(cortex) and youll have tranny control also. that will also help you get better mileage.