From time to time, I use an artist's pen to place eyes on small scale figures where I can never seem to keep just the perfect amount of paint on the tip of a brush. Perfect pupils every time, but I don't use the pen for much else because otherwise I'd find a way to stick my thumb in it and smear the ink.
My local Michaels craft store stocks them alongside a piece of paper to try the pens out before making a purchase decision. Plus, with their weekly coupons, it remains affordable enough to experiment with new techniques or products I haven't used before.