Love this product. I buy one every 3 months.
It's easy to use because it has a felt pen tip that's long enough to work kind of like a calligraphy pen, so you can make thicker or thinner strokes, depending on how you hold the pen.

Stays on all day, good, opaque colour, and only starts to dry out after about three months.
Cheaper than Stila's version - so that's a big bonus!