With my Wow Nuport I have to change cartos about every 2 days - but with other juices they can last up to 2 weeks. I've been told by those here who know that this is due to the sugar content of that juice. I suppose it also depends on how much you vape, whether you are vaping that same flavour all the time, etc.
I
don't like the tanks with the black ends because you have to seat the flange just right into the base of the tank. The silver ones seat anyways.
Vapi, your initial question makes me wonder whether you are actually talking about tanks, or rather the clear cartomizers? These have no polyfil so they look & act a bit like a tank, but they have wicks suspended from the top, and the cartomizer is built in. From what I have read, early versions of these do have issues with the wicks not absorbing quickly enough when chain-vaping, thus burnt taste, and the need to swish the juice around to keep the wicks soaked.
I don't know what accessories you can get for iGos compared to eGos. Egos you can get nifty collars that you screw onto the outer threads, which makes even the 6ml tank look less chunky.
Hope that helps.