I spent a bit of time with one around '96 or so when a friend had it. Moreso than any other Mesa amp in my experience, this one needed to be cranked up to get to the good stuff...otherwise it sounded kind of undefined, dull, even dark/muddy IIRC. Once you lit it up though, it really came to life...a huge, somewhat British-inspired tone that would rattle your fillings.
I'm not sure if it's still the case, but Tom Anderson had one in his office that he used to demo all guitars before they left the shop.