I like the Tow Haul feature, compared to my old 4 speed tranny on a 2000 F53. The downhill engine braking is the best feature. F53 chassis had great brakes, but you really needed them with the 4 speed.
I would not use it all the time. I find the tranny upshifts 2-300 yards later at the top of a hill in Tow Haul (cruise control on). Same on a start from a stop. I maunally switch out to eliminate that extended time in a lower gear. If you have a ScanGuage you can see the difference in fuel use. Anything that reduces transmission heat in city or hill driving is a plus.