Originally Posted by Metaluna

Just eyeballing the pictures of the VO Thumbies, it looks like the boss where the barrel adjuster mounts sits very close to the body of the friction shifter (i.e. the round part that the cable winds on to as you move the lever). It's possible that there's not enough clearance to mount certain brands depending on how they're designed. This could especially be a problem for any 11s road or 10/11s Dyna-Sys compatible shifters. These usually require a larger diameter "barrel" in order to pull more cable per click of the lever (this is actually one of the good things about Dyna-Sys and 11s road standards). I have the equivalent of BS-M10's (10 speed Dyna-Sys compatible) on my Gevenalle shift/brake levers, and the round barrel part is noticeably fatter than both my old 9 speed Shimano barcons, as well as some 9 speed Microshifts I recently acquired. It's plausible that they would not fit on those thumbies without modification. Or maybe they'll fit, but the cable exit angle will be weird or something. You could try filing them down a bit but there's not much metal on that cable stop, and for the price they're charging, I wouldn't risk it.