It will give you more available power, but only when your foot is on the floor or close to it. How often have you felt the need for more power?
Fuel economy.... it will help a little if you're towing a pretty darn heavy load. If you're unloaded, it most likely won't make any difference at all. All their published results are for very heavily loaded trucks. I've asked them directly, "What will it do for mileage when you're driving around normally with no load?" They hem and haw and say, ".... possible increase...." but no guarantee.