The practical tradeoffs all cut against fountain pens: they run out of ink quickly, they dry out quickly, the ink smudges until it dries, the ink will run or be erased if the paper gets wet, they are very sensitive to the quality of paper, they can leak easily in your pocket, etc.
Nonetheless I have several fountain pens, and I enjoy writing with them. There is a bit of ceremony about it. It slows you down somewhat; this is good. It's rather like kneading bread dough by hand instead of plopping the ingredients into the bread maker and pushing the button. It puts me in touch with the craft of writing instead of its mere utility.