Cooler is a cooler, they both work the same, cool the cpu. I've run my pc's for almost 24/7/365 on AIO's, my kids on Air for over 6 years. Nothing but Air prior.
Time used isn't the issue, workload and appropriate cooling is. Just get a cooler that's larger in ability than what you think is necessary and nothing you do will overheat it.
AIO's suffer pump failure and leaks. BS. It's an electronic/physical component. Everything suffers a certain percentage of failure, psus or ram even mobo's or cpus. What you hear/see on the net is the 1% of failures. In 30 years of pc building, tinkering, fixing I've had just about everything fail, sometime, someplace except for the aio. I just last week replaced my 6 year old nzxt Kraken X61. Not for leak, not for anything due to pump failure, but the fans died.
Most all aio failures are due to owner twisting of the tubing putting undue stress on the connectors, in effect creating the leak. Not wanting to admit to user abuse, they just blame the aio leakage on the aio/manufacturer.
And then others (who have no direct experience with leaking AIO's, just repeat the BS.)