No real long term experience. They opened a B20 co-op type place right across from where I work so I tried it for 3 tanks. Over those 3 tanks, I saw ~1mpg drop in mileage and I was paying the same or a little more than the normal place I filled up. As far as performance, I didn't notice much change. THere was a slight change in exhaust if I remember.
\'05 Chevy 2500 HD LS CC/LB 4x4 D/A, Century Cap, Line-X Spray on bedliner, SS Nerf Bars, Lund Bug Deflector, 235/85R16E LTX M/S II, Kennedy Custom ECM Tune, Uni-filter, EGT/Pyro & Boost Guages