I have a red ring artpen, and was very happy with it at first, but I was really glad I switched to dip pens. I still use it occasionally, but sometimes ink spurts out.
The most obvious advantage of dip pens, is the cost. For less than an Artpen, I can buy ten nibs and a holder. This is important because nib width determines size of the letters.
Second, changing colors is much easier with a dip pen. You just wipe off your nib, and dip in a new color. You could also have two different nibs the same size, in two different holders, if you keep switching back and forth between colors. With a fountain pen, you either have to deal with a converter or cartridge. With a cartridge, once opened, they don't really close. There are also some standard sizes, but some brands use different ones.
I haven't used a converter, but I understand you can, return the excess ink to the jar, which must be nice.
Third, and most important, I find that hairlines are much easier with a dip pen. Maybe it has to do with the ink I used, but my fountain pen rarely left enough ink to drag.