Honestly, nothing annoys me more than "one size fits most." There is a vast disparity in heights, weights, shapes..."one size fits most" is basically a bullshit measurement. Even if something is adjustable, it's bound to be too big on a good number of people and too small on an equally good number of people.
Er, that rant is directed at Cal Ex, it's directed at all companies that use "one size fits most." If you're going to say "one size fits most," at least include the actual measurements of the product.
Just speaking from personal experience: one size fits most tends to be too big on me; I'm a B-cup, 5'3", 115 lbs. But it tends to be way too small on anybody above 150 lbs, 5'6", or C-cup breasts. :/