I tried the whole SS family (no Fusion) together before buying my MB800.
As you'd expect, the MB800 had more than a little extra "something". Still, at reasonable volume levels, the family resemblances were more striking than the differences. The aux in on the 200 is a great feature for practice, doubling at small gigs, etc., as well.
The only thing I could see you missing compared to the RB, is that I haven't managed to get a good imitation of the dirty sounds I hear people getting from the RB700-II. Of course, you'll get more opportunities to drive the MB200 hard, than I do with the 800 and a measly 500 watt cab.