Possibly my own fault for not taking the description closely enough, but they recommend not leaving these inks in your pen if you're not using it every day. I often go several days without using my pen, so using these inks would be a wasteful hassle.
Doctor_MemoryAs a horrible person, I've had the green in my pen for ages, then the brown. Doesn't seem to be a problem, though if you let the nib dry out, you might have to take the pen apart and clean it. I use my pen once or twice a week.