I have had the MB210 for about six weeks now. I had originally selected it over the MB212 because of the ability to add an ext cab, i.e., scalability depending the needs of any given situation, but most of the time only needing the combo for personal practice and band rehearsals.
I did discover, however, the low B string causing some farting at higher volumes during my first full band rehearsal with this thing. I figured it was too much for the 10s.
So, my brain has been hurting over reading all the threads I could stand here and on other websites on this topic. I was exploring adding the MBE115 or swapping out for an MB212. Then I discovered all I had to do was dial back the bass on the EQ and voila - no more farting, but still plenty of low end. Problem solved.
Also, I think I won't need an extension for bigger gigs because bigger gigs require PA support. Cranking up the volume of everyone's amps will be more difficult to achieve a nice live sound mix than handling that with a decent PA and sound guy.
MB210 is more than enough, plenty of volume - it rattles windows and pictures off shelves and walls. If your band is drowning you out during rehearsal, then they need to turn down or you'll all go deaf!
I hope this helps someone having a similar experience with the low B through the MB210.