I've always wanted to like the space pen cartridges, but in my experience they have always seemed kind of bad at writing. Compared to, say, a disposable Bic ballpoint it writes a rough, gritty, inconsistent line and tends to leave - and worse drag - little flakes and strings of ink that look like eraser debris but stain like ink. Sure, in microgravity or underwater it works when other types would fail, but I do so little writing in space these days that it doesn't make much sense.
For pens to carry around or use at the house I've gone back to cheap or free ball points, although I do keep an inexpensive Pilot Metropolitan with a medium nib loaded with Pelikan 4001 Royal Blue ink on my desk at work.