I have a B2M that I use with a Roland XV-2020. It's main use for me is to sound like a cello, and for that purpose it does nicely. There is a heap of great sounds, IMO, in the XV-2020 but not all lend themselves to monophonic playing, which is what the B2M gives you, and I'm not so sure a monophonic clav would be so great: Not too many keyboard players get by playing one-fingered...
For that purpose I've been working towards an Axon AX-100 + Roland GK-3B pickup, but I'm not quite there yet. Some cool things I'm looking forward to trying out once I'm finally polyphonic include harp & classical guitar, which sound great on the XV-2020 but monophonic just doesn't sound right.
As other posts have said, bass to midi is not for everyone. But if you can afford to start with the B2M & XV-2020 as I did and take (or leave) it from there, by all means go for it.
Peter
Ballarat Australia