My X9s are three and a half years old and have been used almost daily, no problems at all here. My only complaint is the fiddliness of replacing the rear cable, but then I run a full length outer and it’s a once a year job at most. When replacing cables I do lube the shifter mechanisms and have had no issues with stiff shifting that can’t be put down to dirty cables and/or poor cable routing.
I have to echo comments made on here about the weak spring on the X9 mech though.
I like my X9s a lot, ergonomically I prefer them to the SLX shifters I run on bike #2. That said, SLX is a LOT better than Shimano of old and SRAM’s influence is clear.