Glocke..I have the Boss ME50B so here is my take on it.
It has rotary controls so we can relate to settings as opposed to pressing buttons to adjust the parameters.
The left side is filtering, the most useful setting(and this is my personal opinion) is the de fret..it gives the bass that nice lazy yawn sound.
The octave parameters are both octave down and up, the down is the best, adjusting the effect gives a nice fat low sound.
The mid and bass selections are good for changing tone without altering your filter settings.
The envelope(wah) are pretty good for the 'bootsy sound'
The synth/drive section has all types of distortion, the overdrive is really good for that grungy sound, I don't use the big muff or metal as they can be pretty severe but if that floats your boat then go for it.
The synth sounds are diverse enough, combine them with the octivider and you can get some nice Oberhiem/ARP bass synth sounds.
Delay/Modulation has tap delay and reverb, the flanger/phaser and chorus all work very well, I particulary like the flanger as it gives 'roundness' to the notes..a bit like the defret but with more intensity.
The compressor section is excellent if you like to use them, you can sustain a note for infinity!.
Pedal assignment is good for alteration and effect on the fly.
The EQ section is comprehensive especially the mid frequency control which I think maybe like the filter/CVQ on S2 basses.
Of course you write your own patches as well but there are presets in there to try out.
The tuner is very accurate.
All in all it is a great unit, years ago when multi effect units like this came out they were good at only doing one or two things and not good at other and people went back to individual pedals, with this unit BOSS have got it well sorted as it does everything well.
It dosn't come with the power supply but I don't use one anyway, I use high quality rechargable AA batteries(it takes 6), the reason is I got sick of loads of cables on the floor, I also use a wireless system.
The batteries last two gigs but I charge them up prior to a gig.
If you buy it also buy one of those aluminium tool cases with the foam in as it sits in nicely for transportation.
