Is there a store near you that carries both the MB210 and MB212? The 212 seems to be harder to find in brick & mortar shops for some reason. Hearing the 2 side by side would probably tell the story for you. There's very little difference between them as far as size and weight, but no comparison in terms of tone...the 212 just sounds much bigger, clearer, and louder to my ears. Yes, the 210 will allow you to add another cab, but the 212 might very well cover your needs with a single box.
I tried a new MB212II at Sam Ash in Hollywood just yesterday. Sounded great, but it's hard for me to compare to my own because the instrument, room, and everything else was different of course.