I'm throwing in another rumble 500 vote. They are stupid light, sound good, have many different tones available. It hits pretty hard for a 210, and you can always add another cab, a 210 or 112. The overdrive is decent as well.
The GK MB does not have the same "GK growl" that the 400rb and 800rb were known for, since that tone was largely due to the Poweramp going into soft clipping (hitting the rails they say). The MB series is class D, different animal.
The ampeg ba210v2 is much heavier than the rumble by the way.
I'm just using a rumble 200combo and a 112 cab and it really has been working well. It is louder and tighter sounding than the 150w peavey 115 combos (rumble 200 is 140w 115 on its own), and easily 1/3-1/2 the weight. Modern technology, plus fender has absorbed several high end bass amp companies over the years, so they learned quite a lot.
Right now it is the best bang for the buck out there.
Talkbass is not a safe place to ask about combos. You will get 90% replies telling you why head and cab is better. Most of those replies are truth,.but not absolute truth considering how light the rumble is. All you lose is the flexibility, you don't lose power or tone, and you save money. A rumble 500+210 or 112 cab is enough for almost anything. I see you found the rumble thread too. Good mix of guys, from newbs to pros, total fender fanbois to people who just stumbled on how awesome the new rumbles are. Personally I was almost exclusively pre fender SWR the last 18 years. Some thieves finally changed that for me

but I am very happy with my rumble rig, which didn't get stolen.