PJK, my (limited) experience is that they are pretty easy to fill, I use a dropper, because it gets in between. I have found that when they get low, they taste lousy, and you have to kind of shuffle them to ensure that they are wicking right.
The other thing that I learned,
through trial, error, and reading here, is that when you are changing the heads, its a good idea to trim the wicks on the bottom about 1/8 of an inch. I had a real issue with a horrible burning taste, regardless of the ohms of the head, and I was ready to give up, but I trimmed the wicks (and put small notches in the silicone cap, but that is another story) and they seem to be working better.
I am still looking for another alternative, maybe the new Kangers, but for now, that is working for me. Hope that helps.