I don't understand the appeal of the Bisonics. To each his own, but keep in mind that both Jack Casady and Phil Lesh quickly moved on from them and haven't looked back. People want to recreate a sound they left behind about a half-century ago.
Probably not much to it, Dave. Jack and Phil were both using modified basses through fairly unorthodox rigs. If they were using bone-stock Starfire II basses then there might be a bit more of a case there, but they weren't. Probably there are bits of:
Nostalgia: these pickups were hard to find for the longest time. We know Phil, Jack, Berry Oakley, Chris Hillman and co all used them, but you couldn't go into Guitar Centre and buy the same basses. Dark Stars (and Novak's reproductions) are expensive and therefore only available to a fairly exclusive breed of bassist, which feeds the idea that they are top-shelf pickups. Curtis Novak perpetuates the notion of 'doing it right' with his work, and the notion of Bisonics being complex and difficult to reproduce sort of helps this idea along.
They look cool: Daguet Guitars make a perfectly accurate Bisonic replica, that deletes the fiddly pole adjuster system and complex plastic flatwork/skeleton. They probably sound spot on, but people don't seem to be excited about them because they look more like generic bass single coil pickups:
Guild got rid of them: Guild phased them out and started using hot humbuckers in their basses instead. Musicians tend to buy into the idea that "the older X was the better X". People think that older 'silver screw' Boss pedals sound better than their modern counterparts, and this is within the realm of cheap, mass production stomp boxes! Again the fact that Guild moved over to different tech feeds the exclusivity of the original pickups.
Maybe they sound alright?: I've only played one vintage Guild bass with an original Bisonic. It was a transition M85 bass with a Guild 'bucker in the bridge and a Hagstrom Bisonic in the neck. The bass had a push switch that either cut all the treble or all the bass from the neck pickup, so I couldn't give it a fair hearing.
Seemingly the Guild reproductions aren't correct, but then again the Dark Stars weren't correct either. I've played a Newark Street Starfire II reissue, and it was perfectly nice. It had the same neck as my Dearmond, and the fit and finish was similar. The pickups seem to be a bit 'honest vanilla' in my playing. Everything and nothing! Maybe this is the appeal of the Bisonics? They have quite an uncoloured, broad tone that pickups up dynamics?
My Guild BS-1 bridge pickup won't fit the Dearmond. The trim ring collides with the bridge! I would need to build my own pickup rings that aren't as long as the Bisonic rings, but as wide, because they need to cover the Dearmond pickup route. The Bisonic ring slopes, and has a pronounced roundover. A total piece of work to reproduce.