I am a pedal junkie, I have the Boss ME50B coupled to a Zoom B2.1u and a Behringer Bass driver.
The reason is so I can use them as
a) tone switching options
b)multi combination which cannot be attained with a single effects processor(but not to overkill the sound I might add)
The Boss unit has rotary controls which I prefer to push buttons, it is a good unit but I must admit, the Zoom has a lot more in it for less money than the Boss, the delay/echo/reverb options are huge on the Zoom and there is a harmoniser, pitch shifter, ring modulator plus a drum machine and USB connection with Cubcase VST software thrown in.
Plenty of choices out there