I've been putting some time in with "Big Green" today... It's definitely not doing what I was expecting it to, but it's kicking butt on other fronts!
The top toe-controlled knob seems to blend in fuzz with your original tone (but with frequencies rolled out determined by the crossover control). So, counter-clockwise (green led zone) has very little 'dirt' and either has your instruments full sound- or variable slope treble cut out if you dial the crossover back from full open. As you crank up to full-clockwise (red led zone), the dirt gets mixed in (the intesity of dirt is determined by the side 'gain control' which adds from zero dirt up to a
lot of it!!!)
The frequency response changes quite a bit when using the toe control.
I wis that the controls were changed- the side "gain" knob adds distortion/clipping without much volume increase - awesome! I wish
this was the toe-controlled knob! Maybe a mod is possible?
If you set-it & forget it, ther is a whole slew of great sounds available! They just take a minute to dial in & require bottom panel access.
I'm really digging an all-out super-Muff like tone that it generates. Think Russian Big Muff, but with the lows intact & more mids! Very crunchy & infinitely useful. Volume & gain are independent, so it's pretty easy to find a sweet spot. Unity gain between bypassed clean & engaged crunch is even possible without low-end loss!

I think my Bas Big Muff might be retiring.
Big Green can also do very legit Sly Stone-esque old-school fuzz sounds. The tone control, on the bottom panel, gives a great range of bright to dark fuzz. All settings are usable and I quickly found some accurate 70's era fuzz!
I'll post more as I use it more. I thought I was happy with my EH BBM for all-out fuzz modern tones... Think again!
Big Green is big. And heavy! It uses standard 9v boss style power or a battery. It appears to be true bypass. I looked hard at the circuit- the switch is 3pdt & the circuitboard traces indicate tb potential. The noise floor is ok. There's definitely some hiss at high gain/mix settings, but you cant hear it while actually playing.
I really wish that all of the controls were mounted on top or on the side. The recessed side knobs are cool, but a little inconvenient. The bottom panel trimmers are soooo important- I really wish they were on top! Also, for my own personal needs, I wish that the operation of the toe knob & gain knob were reversed. Real-time control of the
gain with my foot would be killer!!!!
Sound quality is really great. Big Green has one of the more 'natural' fuzz tones that I've heard. Not synthy at all. It's definitely not overdrive, but more fuzz-meets-saturated distortion.
I kind of dig the aesthetics. Definitely takes up some real-estate,.. but I think that's part of the charm! Plus, you can pretty much jump up and down on the thing- it's
solid!
***full disclosure: I received this pedal free from Fender. I'm making every attempt to be objective, but just so's ya' know!***