If you are looking at the Poly Blue for the fuzz, I’d caution you to keep your expectations low. With the fuzz engaged, the clean signal disappears, and the fuzz itself is not broadly applicable on bass, if I were to state things delicately. The modulations are good, if lacking in controls, and the octave up is pretty chime-y. The octave down, when set to mono mode, is about as glitchy as an analogue octave divider (it’s up to you to decide if that is a good or bad feature).
I don’t own the Poly Blue any more, so I can’t directly compare the two, but the tone of the mono mode on each is very much in the OC-2 vein, though I prefer the tone of the OC-5; the latency in Poly mode felt longer in the Poly Blue, though it might track complex chords better. The octave up on the OC-5 sounds better to me than the one on the Poly Blue, and it can do the “track only the lowest note” trick in poly mode. In general, I’d say the Poly Blue is better suited for guitar and many of its features are lacking when used on bass, while the OC-5 doesn’t really lose anything when used on bass, and has the better sounding octave down and up.
