The pen itself looks like any other felt tip pen. You remove the cap and it has a pointed felt tip. Pretty simple really. The tip is pretty flexible, but not so much that you can't get a decent line. From the swatches below you can get an idea of the thickness of the line it produces and also how easily the pen can be manoeuvred across your skin. It doesn't stick or drag unlike some other eyeliners I've tried.
The colour payoff is also pretty good. It's not a deep dark black on first contact, but if you go over it a second time it looks amazing, and once it's dried, it doesn't smudge. It's not at all waterproof though so that maybe something to watch.
The only minor problem I found with the liner was that there didn't seem to be a steady flow of product from the pen to the nib, and I found the tip sometimes got a bit dry so I had to replace the cap and shake the pen a bit. Not a major problem, just a small annoyance. For £2 this is an extremely great eyeliner and one which I would happily repurchase.