Get it dialed in, build you patches and you can cycle through them with ease on the fly. Tuner is excellent and fast, sounds great, and the selection of effects is fantastic. It could use a built in expression pedal like the guitar version gets, but there is an input for one.
My only gripe, is the displays are somewhat smallish, meaning we have to really focus to make sure I am picking the right effect... But those with 20/20 won't have an issue...
Zoom B3 Bass Effects and Amp Simulator
Bass Multi-effects Pedal with Stompbox-style Controls, 12 Amp Models, 99 Effects, 100 User Presets, USB Connectivity, and Bundled Software (Mac/PC)