I've built Aion's Zelus Fuzz, similar to the Bayonet, Blackout Effectors's version.
It doesn't sound bad, but I find the controls very tidious to find a good setting. Tone control interacts with the Mids control in a "bad" way : Tone won't impact the sound very much, as long as Mids isn't set at high value.
Pre-boost and Sustain aren't easy to combine either, and they aren't very interesting or effective through their whole rotation in my experience : at low settings they're useless.
Focus allows to choose between more bass or more treble in an interesting way. Probably the easiest control to use. But it's weak : on bass, you can't really have a bass boost this way, you need to turn up the bass on the amp's EQ. It feels more like a powerful Treble cut.
Once I've spent some time turning knobs, it's able to produce a warm rounded up and colored sound, with a mid emphasis.
It's a good circuit, but compared to the Ram's Head or the Op-amp... I was disappointed. It feels like a bland muff version, with a mid control to give it some more taste.
My first stompbox was the Metal Muff. I don't use it a lot, but I find it much easier to shape the tone with its EQ controls. At least you don't need to crank up Mids or Tone to get something from the other controls.
Metal Muff is sharper, colder and more "aggressive" than the other versions. Reminds me of some Mesa triple rectifiers emulation from Wampler. There's a sparkling coldness, like in PPCB Pathogen.
You can find some kinds of Rat tones when you tweak the EQ.
I find the Op-amp, the Ram's Head and even the Blackout effectors versions easier to incorporate in various styles of music than the Metal Muff.