It's a great synth pedal. The only other synth pedal I've owned is the Boss SYB-5 - the C4 does all those sounds and countless more with very low latency and good tracking.
Using it to replace an Octamizer and MXR M82 is a slightly more tricky choice:
Octaver: I'd gone through a lot of octave pedals to get to the Aguilar Octamizer which I think has the most usable and natural (least synthy) octave down tones, also can be ran clean to use as a tone control. I haven't found a C4 preset (yet) that replicates the Octamizer, some things very close though. This isn't a deal breaker as I usually use an Octaver with something like distortion or filter after it so the subtleties get lost anyway.
Envelope filter: It does loads of envelope filter very well. Thanks to Quatschmacher for the 'Purple 2' which is the best I've found at replicating the M82 and is very very close. There's possibly a slight bit of M82's mojo that gets lost- perhaps that's down to the limited hands on control, or is me being sentimental and I'll just need more time to get used to it.
The main issue I can see is that to fully replace my Octave and filter pedals like-for-like would need the ability to click with my foot for either/or both - I'd need an extra footswitch (like disaster area micro midi), a workaround is I have 3 separate toggle switch presets assigned (filter, octaver, octaver + filter), it's not quite the same as clicking by foot though. And to get all their knob controls to hand I'd also need some type of midi controller.....price creeps up and any pedal board space saving gets lost.
Also has:
Distortion: Good range of distortion, probably won't be replacing any of my distortion pedals but is decent enough.
Tremolo: Can work well as a tremolo pedal, I'd like time-based effects like echo but they don't seem to be an option.
Quatschmacher's Upright sounds.
....and probably loads of other things I haven't found yet.
The C4 is a certainly a keeper, a great synth pedal. It doesn't fully replace all the hands-on control of separate Octaver and Filter pedals but adding some additional control pedals could mostly solve that. I guess in my ideal world the C4 would have some extra mappable knobs, and an extra footswitch or two go through presets - obviously that would make it bigger and more expensive though and can buy those controllers separately so can't really complain.