Hm. It seems to work pretty well. I made sure to prime it and everything before i actually filled the tank. It hasn't leaked on me so far. As for the cartomizer, I have been reading around this forum and once it tastes "burnt" I have to change it?
If you're using it alone, without the tank. Yep, once it tasted burnt it is burnt. Top off early and top off often. The tank takes care of that problem for you.
But no carto will last forever. You'll know when to put a new carto in; the flavor and vapor production begin to go south after a while. How long a while? Depends on your tolerance of bad taste. To me, 10 ml for a carto alone is tops, 15-20 ml for a carto in a tank.
As always, YMMV.