How similar are they to each other, or are they completely distinct guitars relative to sound, playability, etc.
I don't have either, but I'll offer that they're pretty different sounding guitars. The OOO has a larger body than the OM and as a 12-fret, it's going to have richer bass and midrange notes. The OM is similar to a Taylor Grand Concert in size. If set up properly, like all Larrivee's, they'll likely both be equally easy to play.