I too was pleasantly surprised with the taste of the liquid in these carts. The watermelon is to die for. My only complaint is that they are only up to 16mg.
As far as refilling goes I've found a pretty easy method, but I will reinstate that these weren't designed to be refilled. I refill often, but still less often than I would with a 510, yet long before any weird taste appears. I can get away with only refilling twice a day which I love. This is to make sure that filler doesn't burn. Filler is always wet. I bite around the green area just above the white tip to loosen the white tip so that I can get it off with my finger nail. Then take out the plastic washer with a paper clip. Put the plug in the bottom, refill from the tip side onto the filler with similarly flavored liquid, and then put it back together and put the plastic caps back on. I then roll it around a bit, remove the caps and plug and continue using right away. I can use the same cart for a long time this way, but sometimes I just switch to a new one because nothing is as tasty as the liquid that comes prefilled in these carts.
