Review (3/5): Black pen was a throw-away; brown pen is ok.
I have dark brown hair with highlights and the black pen is absolutely useless for me -- it's far too dark to look natural (think black sharpie). I also think it may be damaged because the tip of the marker protrudes far more than that of the brown pen. The black pen also leaks whereas the brown one does not.
I wish the brown pen were a few shades darker. It would also be nice to get two of the same color because I don't understand the point of having a pen that's pitch black and another pen that's a soft light brown -- who would need both of these colors?
The pens do stay on decently. I tested it by going to sleep with my eyebrows on and they were there the next morning. With that being said, the ink easily washes away with make-up remover.
Overall, I'm not sure I'd purchase this again. Unless they come out with different shades and/or the option to buy multiple of the same shade as opposed to automatically getting a mixed box.