The thing I love most about this is how easy it is to use. It's literally like a thin black marker for your eyes. You can go really big and bold, or opt for fine and precise with this pen. It also stays pretty well.
Not sure if it's waterproof though, but do be careful not to make mistakes, because it dries pretty fast.
Unfortunately, the one I bought's inner cap keeps falling out so I end up with black lines all over my hands from opening the lid, but that's no biggie. :)