Looking at some of Mentler's work, it's easy to see parts of the original sketch still showing through here and there - he seems to start with a stick figure and strike in measuring lines to provide accuracy before proceeding to the construction phase. I like this approach, but I do believe it's also important to do the *other* kind of gesture sketches as well - not to be developed farther but to serve simply to aid you in developing the connection between eye and implement. It's been said the point of doing gesture sketches is to take the intellect out of the way - to prevent you from overthinking. To build those direct neural pathways running from the eye to the hand, and to help you to begin drawing impulsively.
Anyway, I haven't done any gesture sketches yet, instead I got all inspired to try to draw like Mentler, who is a sort of modern-day DaVinci:
The fountain pen is really frustrating when I use it in the cream colored sketchbook - the paper isn't slick enough and it very quickly gets clogged with paper fibers and needs to be cleared constantly. In fact, all the little circles and squares and the alphabet were to keep testing the pen and see how well it's working - weirdly it always seems to cut out at the same part of each circle or square or letter.
Oh - forgot about Boldini - in one of the threads about the benefits of gesture drawing someone mentioned an artist named Boldini who's paintings are practically ALL gesture - amazing stuff!!