Cartos make a 2-piece PV and are disposable, obviously more convenient. I refill some KR808 cartos with variable results, some burn, some leak. Maybe it's me. I would use cartos if they cost less. Instead, I'm using 510 attys that last me months to save dough. For the price of 5 cartos, you can get 2 attys on sale. Cartos last 5-10 refills, though I heard some better/expensive ones can last 100 (ask someone else). I go through 20 carts of juice a day, heavy

. If 2 carts hold 1 carto of juice, that's 10 refills a day, about 2 standard carto @ $1.60 each. Others get a week on a carto. Disposable anything usually costs more (I'm old school). The flip side is attys take more time and work.
I've tried blue foam as cart filler, turns cart into mini-tank, holds more juice. Also tried dripping, tops for taste, but didn't like carrying juice bottle around.
p.s. Boodle is right, cartos waste juice too.