I tried the BK5 extensively. I liked it and that was BEFORE the OS 1.05 update which added some useful features. Don't waste your time with the BK3, IMO it's inferior in every way. Most importantly it doesn't have on-board style creation and editing.

I ended up keeping my E50 because it has a built-in sequencer, bigger screen and the style creation workflow had been thoroughly debugged by a generation of G-70 users. But if it ever fails I would definitely replace it with a BK-5 or upgrade to the BK-9. Both sound good and are enjoyable for "real time" play.