these old school ringers typically have an internal arm with a couple of washers that hit the inside of the bell - making the ringaling sound. the little lever is pushed along the edge of the bell, instead of the single flipper that is in the new styles of bells.
i have one on one of my older bikes, and removed from the handlebar it is just as easy to use without it being attached.
from a user perspective, i think all your guests will easily be able use them without any problems. they will probably just stick their finger into the handlebar mount, and with the free hand, or the thumb flick the lever. your guests will have a ball!