If you’ve tried any of the other Big Muffs (or countless clones) you have a preconceived notion of what a Big Muff is. If you’re looking for scooped-mids and thunderous fuzz, look elsewhere. If you’re looking for tons of tweakable options from overdrive, to distortion, to full on fuzz give this pedal a shot.
It’s got plenty of great sounds in it. Sure, it can be a “plug and play pedal.” But there are lots of fun combinations that come about from a few hours of knob twisting. The permutations of combining the two sides and playing with bias, voltage, etc. make for a really fun and rewarding time. You can get huge “singing” leads sounds, thick rhythm chunk, and sputtery-gated-velcro fuzz effects.
The overdrive side is great. You can do faux Clapton treble booster stuff cranking the volume and the tone on the pedal, rolling off the tone on your guitar, and slamming the front end of your amp. Pulling back the tone and gain to nine o'clock and cranking the volume made for a wonderfully touch sensitive drive that responds really well to pick attack. You can also dial it in for “chimey” clean tones with just a touch of hair around the notes.
For me, the OD side is amazing (and even better when goosed by my HotCake or Huckleberry). The distortion side is good in the right settings. It’s good when reigned in, but loses definition when the gain is cranked. I think in general I don't respond well to heavy-handed gain, so it may be a personal taste thing. Both sides respond well to picking dynamics and to variations in guitar volume.
All that said, there are some opportunity costs with this pedal. Dialing in the "perfect" setting on both sides can make for a less than stellar combined sound. And making a perfect combined sound can result in just okay individual sounds. Right now I'm running the OD with it's best sound (to me) and then dialing in the distortion side to make a great combined sound. I don't love the distortion sound on it's own, but it works for the combined sound.
Any way you slice it, $99 for germanium transistors and this many options is a pretty great deal.