Hi Peter
I have only had these pencil mechs. for a week and up to now they seem ok as long as you use Timberbits pens. They don't seem to be happy with pens from other suppliers but I might be wrong.I have for instance used Timberbits Sierra which are ok but using Sierra from another supplier it does not fit. Perhaps some other forum members can give their views on this mech.
If you go on Timberbits site you will find a very good vidio about this.
Glen