You really should wash the bike and clean all debris away from the gearbox before removing any cover that exposes the internal mechanisms and risks contamination.
The grip shift is a good system for the gearbox. Took 2 minutes to get used to. It does not accidentally shift.I've been interested in a Pinion bike and almost pulled the trigger a few times. In the end I'm pretty put off by the grip twist shifting. If they had a thumb shifting system of some type I'd have gone for it by now. Good to know they are reliable and hard wearing. I take it the transition between shifting while pedaling versus while coasting was easy enough to get used to.
It's only for the C Line gearboxes I think. Mine is the P1.18.At any rate, the issue with both the hub and the gearbox is that the shifter operates by pulling a cable in BOTH directions, so standard stuff doesn't work. IIRC, the Cinq stuff is separated on both the left and right side of the bar.