I own a Quattro, the first version, the one with tremolo.
Now I'm moving to g-system, but i have to say that the quality of this unit is oustanding! Built like a thank, I really love the compressor, really dynamic and clean. The tremolo is fine too and in the insert loop I connected a Carl Martin Chorus Xll, a killer pedal!
The distorsion section sounds great with the second channel of my Road King Head, but is extreamly noisy with the others...
The delay is a pure analog eco... I'm not into this kind of effect, I prefer the digital one
In conclusion, I consider the Quattro a great peace of gear (like any others Carl Martin product) and if you are searching for great analog tones, this is the unit for you.