The Muffin to my ears isn't really fuzz - in fact its not even an extreme distortion at full pelt. It has a very open sound compared to the compressed sound of a tube screamer.
Having tried the Muffin in three amps (a Mosfet Session, a Vox Valvetronix and a Fender Blues Junior) I can say that it works very differently in different amps - in the Session it warms up the sound a bit and adds dirt, in the Vox it acts like a plexi box and, strangely, in the Fender it remains relatively clean (which is perhaps an artefact of the Jensen C12N).
I like it, but tend to use it as a tube boost (keeping the gain on minimal levels) rather than a distortion/od pedal.