The Guild BS-1 is a decent pickup. It is actually a Hammon Dark Star tribute pickup, and not a Hagstrom Bisonic tribute. (but is not a true clone of either one).
See here, from Guild:
Th BS-1 can be dialed in to a sweet spot or 2, between amp settings and tone knob. I had a pair of them on my GSR M-85-II, and they were certainly serviceable. I did have prior experience with vitnage Hagstrom Bisonics, on vintage SF basses (and a couple JS/Jetstars), and the reissue does not sound quite like those, but it still sounds pretty good.
I decided ultimately to upgrade to a pair of Novak BS/DS switchable pickups on the M-85, and it did make a world of difference. Novak's Bisonic and Dark Star tones sound as good, or possibly better, than the originals, to me...with zero unwanted noise. He really nailed it! Novak's pickups are (noiseless) clones of the originals, where the Guild BS-1...somehow is not. They must have used different type magnets, windings/coils, etc.
@fronobulax is the only one I am aware of, that still owns both a vintage Hoboken SF-1 bass with Hagstrom Bosonic, as well as a Newark Street SF-1 bass with Guild BS-1. The pickups are in different positions, but the basses are otherwise an original, and a reissue of the original. Perhaps his opinion on the BS-1 is worth the most, to anyone seeking such an opinion.
Serek uses the Guild BS-1, as well as the Novak, in his solid body basses. I've only seem some videos online, but those videos, together with my personal experience, leads me to the hypothesis that the Guild BS-1 has potential to be a really good pickup in a solid body bass. whereas a Bisonic (Hagstrom or Novak) really wants to be in a hollow or semi hollow bass. The Dark Stars (Hammon or Novak) seem to shine in both scenarios. The Dark Star is like a "Bisonic that identifies as an Alembic," or something like that.
Guild did a very good job on the BS-1, for a mass produced, $99 pickup. It is giggable, for sure. The Novak however, takes you straight to the top. total game changer