I've used this product for near 10 years. I love the saturation of colour, the ease of application and the fact that it's self sharpening (ie winds up and down). One low point is the fact that it can break easily and pieces can fall out once the lead breaks.
Another low point is that I don't think it lasts for 16 hours. I'm prone to watery eyes so I found it does smudge and wear off by the end of the workday and needs re-application.
I used to use this eyeliner all the time. I love the wind up pencil and the fact the end is very pointy. The main problem I found with it was that once the tip started getting blunt it was a lot harder to use. It definitely gives good definition and is easy to use in comparison to other pencils. I did however find that it did smudge before 16 hours but then again working in a hot environment probably didn't help the matter :-) I would definitely use it again and I would recommend it to others.
Tips: Carry a spare to touch up a liquid eyeliner in a hurry .... works wonders :-)