Picked up an MD-2 mega distortion for l$30 off Reverb just as an experiment. Wasn't expecting it to blow away the majority of every bass dirt I've owned and loved before, but truth be told, it did. Absolutely insanely great dirt for bass. All gain ranges covered, extreme low end (actually adds lows to my signal), super touch sensitive and a beautiful harmonic crunch like the best JCM800 I've ever heard. There's a video online with it on bass, but it sounds nothing like real life.
I call buying used Boss pedals "candy buying" since they're so cheap. In the past two weeks I've bought a bunch. DIrts include ODB-3, ML-2, MZ-2, MT-2 and MD-2. Except for, ironically enough, the ODB-3, they all kick ass on the bass (for those that didn't read the other thread, the MT-2 and Mantic Vitriol are kissing cousins...they sound identical). But there's something special about the MD-2. Y'all should buy one just for fun. Like I said above, the one I bought was $30 shipped from Reverb.