just to back up Ken's finding based solely on what I've read here (no hands on experience), there have been plenty of threads with people complaining about build quality throughout the MB line of products. sometimes just commenting on cheap feeling pots or knobs, so take that for what it's worth. but not even just the heads, mind you... there's a megathread in the making about the fact that the MB cabs use ZERO batting and bracing. Further, it has nothing to do with the quality of the components or how road-worthy the construction is.
my first big rig was GK (2001RB, 410RBH), and while it was built to feel quite sturdy, it had its share of issues. i've also played through quite a few 800RB's in my day, and known a few of em to blow up. GK in general seems like good gear, and they hit a great price point, but its not "bombproof" like some other companies (Mesa, for example).