I tried a smok carto tank and I have a Youde tank that I can't remember the name of. In terms of flavor, they were always better than, say, a standard Protank/iClear type setup. I'm not so sure that holds true to the next gen clearos such as the Aerotank Mega, but it's been months since I last used a carto.
But there was nothing about them that I find more convenient then a well built RTA such as a Kayfun. The learning curve is greater, of course, but once you have a well built coil, it can literally last for months. Once, maybe twice a weak, a quick dry burn and re-wick and you're good to go. I have that process down to about 5 minutes including disassembly, 10 minutes if I'm feeling froggy and want a new coil.
Clearo's aren't that easy.
Must be a question of perspective and practice then. Ive been using carto tanks for so long I can fill and prime one in under 2 minutes, Refilling is even quicker.