Well the new carts are a different form of clearso's, or ce3's. The ones they carry now are ce4's. Another vendor calls them the pheonix. Do a search for Pheonix clearomizers and you'll see what the deal is. As far as pro's and cons.
Carts- pros- easy to fill and carry around. Can buy them prefilled and avoid the mess. Con's- can burn and taste bad and need to be tossed. Don't hold much
e-liquid. Flavor is lacking because of the poly fill.
Ce3's or pheonix - great flavor and good vapor production. Hold's more liquid than standard carts. Small and easy to fill a few and carry them around. Longer life and can be cleaned. Cons- have to fill with a syring, a specific way. Harder to refill unless empty. Some reports of leaking.
Ce4's or x2 clearomizers- easy to refill, good vapor production, can be used many times. Good flavor, hold more
juice than either of the other two. Cons- some wicking issues. Not as easy to carry around multiples, meaning you have to carry around a small bottle of
juice to refill. Some juices have been known to melt or crack these, but may have resolved this issues with the new plastic.
Also in both of the ce's you can see how much juice you have left. Your expierence may differ slightly and others may have methods that help resolve any of the above issues. I prefer the ce3's because they work best for me, but I use all 3 at different times depending on the situation. Well, once I'm out of my current prefilled carts I'm done with carts. Refilling any of the 3 is also the less costly than buying prefills. If I can help clarify anything or you have any questions, let me know.