I had an me-50 for a couple of days and didn't think it was that great. But my main problem was I already had a boss OD-3 that I really liked and the ME-50 obviously didn't have quite as good overdrive, so I wanted to use the OD3 and the ME-50 at the same time, which made the multi-effect unit pretty pointless! ☹
Also I didn't think the reverb was that great, IMO they'd be better off modelling one style (plate or spring or whatever) and giving you more adjustment range, instead of cramming 4 types of reverb round that little knob so you can't get much fine tuning.
The other stuff on it is good fun though, good phasing and the expression pedal is better than others I've tried and the pitch shifter is a laff, and I liked the humbucker modelling now I think of it. And for the price, if you've got nowt else it's a good investment.
I just tend to use reverb + overdrive mostly, and wasn't mega impressed with those features on it. And you've got to bear in mind that for what it does it's quite cheap, so not the highest spec thing in the world. Good fun tho 😛