Zefiro
Zefiro's brushes pair a bamboo handle with genuine plant-fiber bristles - agave/sisal for dishes, palm fiber for heavy scrubbing - not the nylon or recycled-plastic bristles hiding on many "bamboo" brushes. The replaceable-head design is the point: compost the worn head, keep the handle, twist on a refill. Metal staples hold the bristles and are recycled separately.
How clear are their specs?
Names the bristle fiber per head (sisal/agave vs. palm) and sells the compostable refill heads openly.