This is, simply put, THE distortion pedal for bassists. I've got an old one from the early 80s that I got from a singer of a band I was in, and every time I've needed to turn up and take the lead, the old Rat is the pedal that gets me there. I'd recommend looking for an old one with the LM308N chip - it's worth the extra cost.
It's a solid state fuzz box, so how good can it sound, right? It sounds great! Especially run through a Fender Twin Reverb.
Dial in just a bit of crunch and you can do all the REM/Smithereens/etc sounds you want. Max the Gain and run it through a stereo chorus for a marvelous singing tone, similar to Santana.
Or anywhere in between, with a tone and output level adjustment to make it suit your needs and drop right into the mix without being too brash.
No fancy lights, your most basic on/bypass switch, but this is one of the best distortion pedals made.