I've reviewed several Joyo pedals now and have loved almost all of them...not just because of the price ($40 to $50), but also because of their (apparent) durability and tone quality that would be appreciated at any price. But ultimately, I decided that this is somewhere between a 4* and 5* review, and I just can't give it the 5* review I've given the other Joyo products I've tried out thus far.
* Extremely high output and high sustain *
When I first plugged this thing in, I had it set up similar to any other distortion pedal I would try out with my Les Paul and VOX combo amp - with the dials all at 12 o'clock (50%). Big mistake. This pedal has an EXTREMELY high output. Depending on the Gain setting, I was achieving output parity with the clean signal with the Volume set at around 25%. This isn't necessarily a bad thing, and it's certainly better than having no headroom to set the pedal louder (a frequent criticism of the BOSS DS-1), but it's something to be aware of.
Also, I read several comments here that this "isn't a high gain distortion". I couldn't disagree more. This thing has TONS of gain. I think people are thrown off by two things: (1) The name, which pays tribute to the MI Audio Crunchbox it clones; and (2) The clarity/transparency of the tone, particularly the higher-end range, that shines through at all Gain levels. "Crunch", in my mind, refers to a punchy, cleanish tone that has just a little bit of breakup in its character. The Crunch Distortion has a tone that doesn't really breakup or get "fizzy" as you turn up the Gain, but that's not what "Gain" really is. The Gain knob increases the saturation and sustain of the note(s), but I think people are fooled by the fact that the sound doesn't crack up. Hit a barre chord and see how long the note holds with the gain turned up. This actually makes the pedal very useful for lead work, also, which is one of the JF-03's strengths.
* The setup is weird, but workable *
Because of everything I described above, you may use some weird dial configurations to get the tone you want. My level is usually around 25% to 40%, and is still very loud. The "crunchy" classic rock tone that other reviewers talked about does exist, but only at around 5% to 15% of the gain setting. And I had the tone knob generally working from 9 o' clock to 12 o'clock, as it got a little too bright to go any higher. (Again, this is with Les Paul humbuckers.) Ultimately, what I decided was that this pedal has enough bass, not too much in the midrange, and very distinct high end frequencies that come through very clearly. If you play gigs and are having trouble cutting through the other instruments, I'd imagine this pedal would do the trick!
* It's costs less than half of many of it's true "competitors" *
While the affordability aspect is distinct from "quality", it cannot be ignored. Part of my initial disappointment was based on a side-by-side comparison with my MXR '78 Custom Badass Distortion. The latter did have a fuller sound to it, and was arguably better for rhythm work. But that's an $80 custom shop pedal from MXR. Try comparing this pedal to a $40 Boss DS-1 or MXR Distortion + and it blows them out of the water (in my opinion). I'm not sure want to roll with the Crunch Distortion being the only dirt box on my board, but if you used it with a specific purpose in mind (like a lead/gain boost), you could afford this and Joyo's excellent "Ultimate Drive" overdrive pedal for still less than most boutique or even BOSS distortion pedals go for.
UPDATE - About a week into owning this pedal, I did revise this score from a 5* to a 4* rating. If you graded the pedal in a "vacuum", I could absolutely see a 5* rating for the $40 price tag. But ultimately, there are just a few more problems and quirks about this pedal that I haven't had with other Joyo products, so the score should reflect that. Please note also (which I didn't realize before) that the internal trim pot for "presence" is NOT easily accessible unless you are prepared to remove the circuit board and the three jacks that are connected to it. A distributor confirmed for me that this is necessary if you want to make the adjustment, and I have no interest in trying to take apart fragile components for a small change that might not even do anything.