Excellent question. I loved my old RB5s, but never got a chance to play the BH5.
I think the reason I never pulled the trigger on the BH5 was the 35" scale. I have no difficulty playing 35", I just prefer the timbre of 34". That's the biggest reason I went from a Lull P5 to a Sadowsky P5.
One of the features I adored about the RB5 was the asymmetrical neck profile. Also loved it on my old MTD 535. I wish every manufacturer offered an asymmetric profile option, but sadly few do, so I settle for standard (symmetric).
A feature I did not like about the RB5 was the locking bridge saddles. It's a good concept I suppose, but execution was poor: locking the saddles changed string height. You can imagine what fun it was to intonate.