MPS!!! The best!!! Shifts faster than any foot could ever shift. Improves times & you're in the next gear at the touch of a button!
Another one to consider is the Pigel all electric shifter. Costs a nice penny but well worth it. All electric so No air to worry about & it also does up-shifts as well as down shifts, 2 separate easy to reach buttons...one above the other. Very handy for road racing (if its allowed)......would have got that one but I drag race & no need 4 downshift.