I've owned both the MB 210 and the 212 combo amps from GK. I had the 210 for about a week, then resold it. That's after I had purchased the 212 and decided to have a try at the 10" version due to its ability to use an extension cabinet. For me it was night and day as far as the quality of output and the volume. The 210 seemed to max out early in terms of putting out a clear but volumnous sound, whereas the 212 was like a Lambourghini: just kind of asking for more and more as you pressed it.
The 212 is ALL I use for my gigs now, which generally involve lounges and outdoor concerts, etc. For larger gigs I run into the PA subs but I'll tell you: that 212 is good enough for most indoor situations, both as a monitor and as a general output amp.
Pro musician since 1968--R&R and blues.