I never had a fuzz (except for digital simulations in multifx). I was attracted by the reviews online, and the possibility to mix the octave (and also by the killer artwork!), and I wanted to add a different character to my pedal board (I have a Keeley Tone Workstation with two overdrives).
Pros: tone is great, with tons of available gain. The tone control allows to shift from Big Muff to more modern territory. The octave is handy, although it works better on high notes with the neck pick-up: sounds a' la Jack White...while without octave you can easily get into Sabbath land!
Cons: quite noisy, and the volume/level control is not really effective. Gain is high even at minimum fuzz level, so dont expect to use it for delicate distortions. I have not tried it with 12V, the reviews mention it would increase volume and headroom.
Note of caution: be careful where you put it in the signal chain. A compressor afterwards would kill it, while a low gain overdrive changes its tone pleasantly.