Other than the physical size and cost*, is there any other reason to
choose between a unit with a main switch +RCBOs and a unit with main
switch +RCD +MCBs?

Need to fit a consumer unit in a small space and very restricted on the
length (though depth and height not a problem).
*Only needs to have 1*6A, 1*32A and 1*40A, so the cost issue of RCBOs vs
MCBs isn't important.