I bet 99.999% of us here don't build basses, so we have to deal with whatever we buy. I haven't come across any bass with flat pickups that don't give more or less bad string balance. But I don't think they've had 20" radius, which must be quite uncommon (I'd really not want such a flat board myself).Maybe good for fans of tiny fretboard radii. Not me. I build at 20” radius, so no problem.
Now, if you build basses, I still have a hard time understanding how a "tetris" rout for a pickup could be a problem compared to all the other routing and woodworking involved.
