Hi RiffRaff,
I also have the BB preamp. To compare with the Zendrive, the BB sounds kinda fatter, the Zendrive just leans towards Dumble-ish tones. As a clean boost, I'd like to take the BB. It's easy to get a crunchy tone with the BB, but the Zendrive is kinda hard to do that. The BB is a very versatile box IMO, If I could grab only one pedal that would be the BB.