This lovely PCB is inspired by the fuzz side of a Fender Fuzz-Wah.
The huge one they reissued later.
Instead of a gain pot it has a Mix control that adds your clean signal to the fuzz.
So its also pretty good to use with bass if you don't want to lose your punch.
Its not to heavy on its own but the "More" switch adds a extra gain stage (not in the original) that will add a lot of extra gain and some lovely filthy oscillation.
V2 fixed the issue with V1 and has a slightly different (nicer) "more" stage
You can also get this as a kit from Musiking here