Mark One is...
Minimal. No superfluous details, not even a visible logo. Clean, simple, elegant, and it comes in two colors.
Durable. The entire pen is made out of metal, and coated with a robust ceramic polymer coating, which gives the pen a great feel in the hand.
Retractable. We wanted a click pen for our favorite refill, and we went to great lengths—including a custom mechanism—to make it happen. Satisfying as heck to click.