I have one and appreciate the depth of sound sculpting it is capable of as well as the ability to deep edit parameters via a phone, but relative lack of hardware controls and therefore the need to adjust using a phone/tablet/computer (via hardwired connection, which I hate) tends to bother me enough that it often doesn't get the job for me. For someone who wants to tweak everything at home into perfect presets or already gigs with a tablet or laptop I could see it potentially being great (or for those who don't want to tweak and just want to download user presets, of which there are lots). I personally like to be able to tweak sounds with ease as I'm playing and not willing to rely on a hardwired computer app for that- it just kills my creative juices except for occasional home recording purposes. Of course I will always prefer a simple analog-style interface with a knob or switch for every function for sound creation purposes and that isn't practical in an FX pedal, but just a little more onboard hardware knobs would go a long way for such a dense device. Also you are limited to only 6 presets accessible on the pedal itself, and no direct MIDI interfacing unless you have a MIDI controller that can operate as a USB Host (only a few can) or else you need a separate dongle to add 5-pin MIDI.
Soundwise there is a lot of good in there, and honestly the editing interface is pretty easy to navigate if you understand subtractive synthesis. The synth waveforms are legit and the analog octaver emulation can sound pretty killer for a digital device and is super tweakable. The filters sound good but lack full ASDR envelope adjustability (apparently due to running out of space during the code-writing, so not something that firmware will ever update unless they start with new hardware), which is unfortunate as the envelope response presets are sometimes lacking for sounds I am trying to match. They are adequate for generic envelope responses, just missing that extra 10-15% of tweakability. The filters also cap out in the high-end before the full frequency range of a guitar or bass, which can be a bit of a drag. The C4 tracking is pretty dang good, but there is still the inevitable latency the lower you play on any of the tracking voices (no latency from the filter or distortion engines).
Honestly the newest update to the Panda MIDI Future Impact v4 makes me more likely to recommend that one for this purpose (the previous Future Impact v3 was about on par for me with the C4, with each having advantages and disadvantages over the other)- the only major downside there is that the editor only works on a desktop or laptop via MIDI interface. So major editing parameters like waveforms, filter types, etc can only be edited in the software on a computer and a phone isn't even an option. That said, the hardware adjustability is quite a bit more powerful than the C4 (one editing knob, but ability to select many different parameters to tweak and even resave with new values), the tracking is faster and more accurate than the C4 (as of the latest updates in FI v4) and the overall tweakability is far more extensive (though it does lack the analog octaver emulation of the C4, I still much prefer analog pedals for that anyway)- he's also added CV and MIDI outputs so you can use the Future Impact to play external synths which is pretty killer.
