I have yet to find a true "pen" in the fingernail polish. The pen is simply a tube with a brush on the end so I think you might be disappointed. I could be wrong though so I will have to see the next time I am in Wally world. My wife sells AVON so I have my pick of lots of colors. As long as I don't get caught anyway.
As for getting a smooth finish, I use my jig turner to do it and thin it down if I can. With the jig turner I was getting mirror smooth finishes. Is why I want to find the materials to make one that turns 10-30 jigs individually at about 10rpm. I think such a jig turner would work with acrylic and vinyl paint.
I love taking my kids fishing, now if I could just manage to fish at the same time.