I haven't tried the CE2's yet, but I do use 510 cartos almost exclusively. The filler materials is very tightly packing in the carto, and I have broken a few trying to remove it (if you remove it you can use the carto to drip, and can drip like 10-15 drops without leaking). Therefore I would not recommend trying to replace it with anything. Also the wire is vertical and comes right up the middle of the carto. It's wrapped in a wicking material referred to as a "sock", it can also be damaged very easily if you start messing with it. Filling cartos for me is super quick and easy. My method is to take the shorter of the two caps and fill it almost all the way up with liquid. Then, take the carto and shove it into the cap (mouth side down). This will force the liquid into the filler material. Then I give a few shakes (like a thermometer) to make sure the liquid is fully in there. To make sure there's no liquid inside the center wire area, I blow lightly on the
threaded end to clear it. Then that's it, ready to go. I've used this method on hard and soft tipped cartos, and it works great. If you accidentally overfill the carto (liquid comes out of the
threaded end while pushing into the cap), then take it out of the cap and shake out the excess. I love using cartos, they're cheap, easy to fill/refill, they work great (unlike carts), one carto normally lasts me almost all day, and I can change flavors whenever I want.