I've had both the B2.1u and now have the B1.on. For the money Zoom multi fx pedals are very good. I found the B2 a little tricky to using given it's only got the 2 digit display on it, the B1 interface is much better. I also own a BOSS GT6B and the amp sims on the Zoom are, in my opinion, much better (but then it is a much newer pedal).
The B1 is great for home practice. Bass in, aux in (iPod, tablet or laptop in) and headphones out. Compact and easy to use.
I tend to put the B1 in front of the Boss, use the B1 for some amp sim and the Boss for other effects, works a treat in a band situation