I am using them tubeless on some Mavic CrossRide wheels. I had a bit of trouble at the beginning with them holding air but according to the bike shop it turned out to be not enough sealant and the valve was not tight enough. Now they hold 30psi for a week at least.
They are comfortable and smooth but they do not have MTB tire edge grip, I almost went down cornering hard over some loose gravel on top of hard pack dirt.
Easy to mount up onto the rim, just a bit harder than a typical MTB tire but not as hard as a road tire. And you can pretty easily get them to seat and pop into the bead lock with a floor pump or even with my single action mini pump so no need to carry a co2 cartridge.
I have about 300 miles on them so far with no issues. I have high expectations for Continental tires and these have met expectations.