Boss recently discontinued this pedal, which is a pity as it doesn't sound half bad. This doesn't really come as a great shock since it wasn't really a big seller. I've found that the DS-1 Distortion and Metal Zone pedals outsold any other. Guitarists generally aren't really adventurous.
One of the unique things about this box is that it has no chips in it. It's chock full of transistors and that's pretty rare for a Boss pedal. The sound is rather gritty, sputtery and similar to the lo-fi sound one can get from a Fuzz Face although not as good. I basically bought it so I can retire the Afro Fuzz since the germanium transistors in it will degrade with extended use. After rehearsing with the FZ-3 for a bit, it doesn't quite cut it so I'm still using the Afro.Back