they are a natural for MTB shifters, if combined with the brake lever or not..
, given tube is 22.2,
and will slide on the open rear end of the tube nicely, last thing..
the big 3 throws front index scheme, just not a personal fave..
but to each their own..

even a Hydraulic Disc brake setup works fine..
Magura HS33 rim brakes on one bike, here.

or Avid's speed-dial MTB brake levers, as on another..