Found this on TGP from the man himself when he was first releasing it:
Basically, it's an FY-6 with some extra bells and whistles in a "pedal board friendly" enclosure. The official name is the EFY-6, with "E" meaning "Enhanced".
The "Expander" knob has been renamed "Fuzz", and the "Balance" knob has been renamed "Gain", as these more clearly describe what these controls do.
We fiddled with the differential amp and worked out a way to be able to adjust the amplitude of half of the cycles coming out of it. Turn it all the way down and voila! No octave step up! Turn it all the way up and it sounds like an original FY-6. In between you can adjust for however much chord smashing synthy overtones you want. This knob is appropriately called "Octave".
A cross-fade knob was installed between the mid-scoop filter and the voltage divider that used to be connected to a switch labeled "Tone". You can now blend between the two tone settings. Obviously, this knob is called "Tone".
The final stage got a gain boost so that the maximum output signal level is more than 4X the maximum output level of the original FY-6, or more than double the volume.
With the knobs set appropriately, it will sound just like an FY-6. Move the "Octave" or "Tone" knobs away from their limits and you can get tones not possible with the original FY-6.
Unfortunately, Wattson Classic Electronics has shutdown, and while they were around they made very few of these. What brought me to find out about this pedal is that the guys of SUNN O)))) have been known to use this pedal.