I have an ACT-LABS shifter dealy, and it works fine. It detents into gear, so it holds the button down fine.
The issue I have with it, is that no combination of "throttle blip" and/or "cut on upshift" settings work.
If you have "throttle blip on downshift" set to ON, then it will blip on ALL shifts, because it can not distinguish which way you will shift. (as soon as the shifter goes to neutral it says "oh...shifting!" and hits the gas). The result is that you over rev on upshifts even if you physically lift your foot off the go-pedal. (and even if throttle-cut on upshifts is set to ON)
I dont find PC pedals to have enough feel to manually match revs for downshifts, so the "throttle blip" is a good feature, but it cannot be used with a gated shifter or the XRR goes to popcorn mode by the end of the race.