I have a Yamaha BBG5 fitted with the double-pole pickups usually found on a Yamaha RBX375. I had one & liked the tone but not the bass, so this works for me - it's my 'go to' bass & I use it for most stuff. I wouldn't consider this as an upgrade, more a matter of preference.
I also have a BB415 fitted with a John East U-Retro by Howard the Bass Doc (marvellous job - routed both cavity to fit & a battery box plus put on 2 layers of conductive paint unsolicited - thanks Howard!!!) . Again, I'd consider this preference.
I also have a Yamaha (noticed something yet?) TRB1005 Fretless which I've left stock as I don't feel there's anything needing to be 'improved' on it - weeellllllll - really, I'd prefer an unlined ebony fingerboard in preference to the lined rosewood, but that's well outside my budget (unless some kind luthier makes me an offer)!!!
G.