To be totally honest, I'm on the fence about this. The actual liner lasts all day, is jet black and I'd say was pretty waterproof (not sure if it's supposed to be or not)
Using this gives a really neat, straight line BUT I just find it kind of difficult to use. I like the tip of the brush/pen to be a little flexible, and this is stiff. I know it's supposed to be as it's a felt tip liner, I just find it difficult to do a full line. It's easy enough to use for a flick on the outer corner, just not all the way along.
This is available from superdrug for £2.00