In my experience the cartos don't have a problem wicking at all, they just vape until they're running dry, in which case you just have to refill them. Some prefer to top off their cartos every so often between fills, when I use cartos, I never feel the need. They should deliver flavor on ever puff just fine. I do recommend letting the cartos sit for a few minutes, just after filling to let the material completely saturate.
How long they last and how many times you can refill them just depends. The biggest factors in how long you can go before refilling are how often you use your vape, how long of puffs you take, and what voltage you vape at. If you vape a lot, take very long pulls, or vape at high voltage, you'll go through a carto faster than if you toned any of the above down, just like any juice delivery method.
Some juices kill cartos faster than others, some heavy VG juices tend to kill cartos faster than PG dominant juices too. And then there are some juices that kill cartos quickly for no apparent reason. How heavy you vape, and how careful you are not to run the cartos dry are factors as well. And then some cartos will die faster than others for no apparent reason, just like atties. I've had cartos that died the second time I filled them, and I've had cartos that never died, I just threw out when they started to taste funny (which will also depends on juice, how you store them, etc).
As for performance issues, there's really none that I can think of. Cartos are pretty low maintenance as far as juice delivery methods. The only reason I don't use them primarily is because I feel like I get better flavor from Clearos, but plenty of vapors don't think that. Probably the majority, I don't know. Cartos are probably the most problem free system you can use. Filling's super easy, they don't leak much (everything leaks some, everything). There's nothing to pinch off wicking, and they're cheap.