I have a Large Sebenza that I sent back to CRK over a year ago for dual thumbstuds. The option cost only $30, for which you get the additional thumblug, a new swedge cut out of the liner for easy access to the new stud, and a complete cleaning, polishing, bead-blasting, and resharpening of the knife. I live way out in Hawaii, and they had the knife back to me about two weeks after the day I mailed it. Due to the superior design of the Chris Reeve thumblug, I find that openings with my left hand are just as easy as openings with my right (using the thumb only). I agree with Maskwa: the dual thumblugs should be standard equipment on ANY folder, especially one as nice as the Sebenza (hey, my Umfaan came with two!). I definitely encourage every Sebenza owner to go for the dual thumbstud!
Take care,
Fedaykin