Whenever I've heard them at pub gigs I thought they sounded pretty good and quite similar to the AD200B, which is often accused of having the same limitation.
With the passive tone stack set with mids full up, bass and treble fully off, this head is fairly neutral and does convey the tone of whichever bass I've used at low volume. Of course I've only had it for a day but I can already appreciate the raw power of the output stage and looking forward to a proper test on a gig.
I think the Clean switch is an excellent solution to the MK1 one sound character; now it has (at least) two!