Everything below is just my opinion!
Having tried the RG-55 guitar synth set up in PMT, Bristol a few weeks ago for the synth sounds, I thought I’d give the COSM guitar modelling a go in PMT, Cardiff today. I tried the ME-25 and was left alone for quite a while (always the sign of a good music store and a good salesperson, I think) to pedal through the COSM presets. I have to admit that I was quite disappointed with the sounds (my Peavey Vypyr 75 has tones equal to if not better than the Boss) and the experience has finally made up my mind for me – I’ll not be investing in the GR-55 at the moment.
However, I am notoriously fickle and may well feel different after I’ve sold some equipment.