I'm sure Mr. Baudin has his uses for this instrument, and to each his own and all that. Indeed, I wish I had the chops Jean has. However ...
Workmanship aside (which is a thing of beauty, BTW), I think it's quite useless for most. Or at least someone who lacks Jean's considerable skills and talent. I mean, I personally find 5 strings difficult to swallow, but 11 strings? Where other than a solo gig would you really need or want something like this? Again, Jean uses it since he feels he needs it (and, damn, he's got skills!), it works for him, fine. But I just don't get the whole extended range thing, particularly if we're talking 7, 8, 9, and up. I mean if you want that, you might as well play guitar. Again, only my opinion, we all know about those (everyone's got 'em and they all stink! :-))
Not trying to rain on anyone's parade here, though. If an 11 or 20 or 150-string is your thing, have at it. It works for you and that's all that matters. Me? I'm sticking with my fours. I'm about as confused as I want to be with them. An 11 string would probably drive me to shear madness! :-)
alan