Yup...if you're going to drop the coin, clear your calendar and read the mega thread, lots of info there.
I'll do you a favor though and give you the short version
The MB210 is good, the MB212 is on another level entirely IMO. Buy that one.
I own 2 MB212's and an MB112. Before I bought them I spent a lot of time trying out the MB115 and MB210, mainly because that's all I could find of the GK combos, even in Los Angeles. To this day I've still never seen an MB212 in a store.
The MB210 is a good sounding amp, but it sounds boomy to me. You can correct this to a point by rolling off bass, but it still doesn't get the mid range clarity the MB212 has. The 210 will also fart out when pushed really hard. I don't play 5 strings any more but I've heard guys that do have issues with the B string at high DB levels.
The MB212 sounds HUGE in comparison to the MB210. It has a meaty tonal character and presence that sits unbelievably well in a live mix. I've played mine just stupid loud outdoors with a 2-guitar/keyboards/drums rock band and never hit the limit with it. (I use 2 of them linked together now for that purpose, but honestly, one will get it done for me)
ALL of the MB combos seem to be prone to QC issues...you'll see plenty of that in the mega thread. I attribute this to the unfortunate reality of manufacturing in China. My first MB212 was perfect. I played it long and hard for over a year and then a speaker failed (it began distorting - I don't think I blew it up, rather it had a bad voice coil that eventually died). Even though it was a couple of months out of warranty GK sent me a new speaker at no charge.
My 2nd MB212 arrived with a buzzy speaker right out of the box (this is a common complaint). I returned it to Musicians Friend and got a replacement, the second one is perfect.
The point is you might have to go through a couple units to get a perfect one, and while that may be a little crazy, all I can tell you is it's worth it. This is the best sounding bass amp I've ever played through and that is a LONG list.
And every time I carry that little beast in and out of a gig with one hand I am reminded of how miraculous that is.
There it is dawg, my 2 cents worth. Now read the thread.