I have, a few years ago. Great in concept but meh in execution / actual use. The generation I rode would not shift under load basically at all. Maybe they are better now, I don't know. Belts are great but not better than chains IMO. They have to be tensioned pretty high which adds drag / drops efficiency (very very bad in my world), they can be cut by rock impacts (but I guess chains can break, however my last broken chain was in the early 2000 or maybe even late 90's, so not really a thing anymore), belts get noisy in dry dusty conditions (water helps but not for long in those conditions). In my humble opinion a pinion drive is a solution looking for a problem, same with all variations of electronic drivetrains (except in a few specific use cases). I have owned everything from 3X7 Shimano to 12 speed XTR, XX1 Axis and Transmission, Red XPLOR 12 speed, etc (haven't tried the wireless Shimano yet but the paint isn't dry on it yet) and I choose to run mechanical XO1 Eagle. It is lighter, less expensive not if but when I break it or wear it out (I go through at least 1 cassette, 2 chainrings, and 2+ chains a year at minimum). Do the math on mechanical eagle vs transmission and then compare the weight of the two groups. Nevermind I never have a battery die on a ride, have to charge batteries, or worse have a communication issue. My mechanical shifts quicker and much more reliable than any electronic drivetrain especially after it's nasty because I can finesse it if need be.
So I guess you could say I'm not a fan...