OK - the kids are safely installed in the softplay, so here's a bit more about it, mainly from what I've asked Leszek.
There's a drive switch at the input which bumps the signal for passive basses, and a bright / dark switch, too. I think we can guess what that does, but I don't know the specifics. I'll ask.
The EQ is a James / Baxendall tone stack, as used on the Ampeg Portaflex, etc. The lack of a mid knob worried me at first, but I did a bit of revision and I can see that it's possible to boost mids if needed by rolling back the bass and treble.
Leszek replied to say he didn't want to use any semiconductor filters on the amp (this is a bit technical for me, but it sounds like a good thing), and assured me that the mids were nice and clear in the first place, so apparently I needn't worry.
I asked him why there's no ground lift on the DI, and he replied that it's not needed as the DI is on the audio transformer, not an integrated circuit (again, I can't pretend to understand what this means).
As mentioned, there is a 120W valve version of this which is the same dimensions but 3U, and is (I think) 13kg. It sounds interesting.
The amp is available in a few styles, including a vinyl covering and a full flightcase.
I've got a gig on Friday, and an all-day rehearsal on Saturday, so I'll have lots of time to A/B it with the Walkabout...