Careful with these! The plastic tube has the tendency to burn just above the metal/atty. 1 of mine has burned a whole strait through the plastic and I got a lovely mouthful of plastic goodness. Their is also glue on the ends of the wick, sometimes the wick is even glued to the plastic tube so if you pull it off to fill it that way you may end up disabling the entire carto.
Outside of those two flaws I really like them. You can wiggle the plastic off the metal and fill it that way. It snaps right back into the atty part and doesn't leak. They look highly modifiable. The flavor is really good as long as you don't let them run to dry.
They should make these with a metal tube instead to prevent the tube from melting, and remove the super glue on the wick.. Why is it even their? Well it sorta holds the wick inplace ontop of the atty for max saturation. I suppose as long as you don't let it burn dry your not in any danger of inhaling super glue vapor but who wants to risk it?