He doesn't need it for any gigs, but has been borrowing my Mirafone BBb/FF for the last year or so, and enjoying very much playing it at home. However, I need it back now (realising I had better practise it a bit before Gurrelieder at the end of August...), and he's looking to fill the void...
He specifically wants one in the low key - I've made recommendations for F contra (I suggested Rath - their R90 F contra is excellent and he likes Rath basses), but he prefers BBb. He knows that F is usually quite a bit easier to play, and still wants BBb. He's a BBb tuba specialist - he's comfortable on the long tube.
Far be it from me to discourage a true enthusiast, so I'd like to make some suggestions as to where he could look. However, my contra is the only modern BBb trombone I've ever tried, so I'm short of reference points. I wouldn't recommend one to match mine (much as he loved it) - it's not the most tonally stable trombone ever built. The only other modern maker of a BBb contra that springs to mind is Thein - has anyone ever tried theirs? I'm not a fan of the Thein F contra or any of their basses I've run across (only a couple), finding them all a bit hard to focus, but that doesn't mean that my friend might not like them more (and the craftmanship is second to none). I also can't find the Thein price-list on their website any more. Has it become an "If you have to ask, you can't afford it" kind of thing?

Looking at the Miraphone website, I see that they make a double-valve contra in CC, which might conceivably be a suitable option - has anyone tried one of these?
Then - second-hand - not many contras come up used, but those that do tend to be interesting. Anyone got anything out there?