Moving BB designs can feel quite weird to an experienced cyclist. Pedal steer can be significant sometimes.
That's the big difference I found - to the point where I could barely get thing moving. It wasn't long before 'no way on the open road' and 'death trap' starting ringing between my ears. Mind you, that was on a MBB homebuild...so hardly the best example with which to try things out. If rake, trail, head tube angles and steering geometry in general on a conventional dark side bike gets you wondering about how it all fits together, then how it all works on a MBB will send you bonkers.
Credit where credit's due though, these things are not just for car parks - I've seen several MBB's on all three PBP's I've done. I especially remember an interesting homebuild by a Belgium guy in 2007. He seemed to get round perfectly ok. As did LMT OTP in 2015 on his Vendetta. Fair play to 'em. Dual 700 wheels and a shorter chain? Got to be worth a go.
The homebuilders in France seem to like them quite a lot too.