There is a lot of confusion about just what the Catalyst is... is it a clean Booster, an overdrive, a distortion, or a Fuzz? The answer is "all of the above."
What does it do best? Clean Boost, non compressed crunch tones (a la Jimmy Page, 70's Jeff beck) and non-compressed distortion/fuzz sounds... accent on NON-compressed. Other unusual traits of the Catalyst are its tight low end and ability to give both flat EQ and accentuated Mid distortions simply by manipulating its 2-band EQ.
Until the Catalyst, only Fuzzface-type pedals truly cleaned up when you turn down the guitar's volume knob. But Fuzzfaces tend to get unuseably bright for most players as you turn the guitar's volume down. Not the Catalyst. That's something that Jeff beck has recenlty noticed & embraced about the Catalyst.
Catalyst can be a Fuzz/Distortion (with toggle switch set to "Flame" position). Catalyst can be a phenomenal clean-boost, and overdrive as well (with toggle switch set to "Spark" setting)