Octave pedals are my second biggest jones besides distortion pedals. I love 'em and it's rare I do a gig without them. Currently on my board, I have a Mooer Tender Octaver for clean + octave up and a Boss OC-2 for clean + octave down. I love the OC-2's synthiness, and I love that the Tender Octaver can give me a sound that comes deadly close to the sound of an 8 string bass without the baggage of having an 8-string. Used to have one and it was a lot of fun, but I could only use it on rare occasions, and I was stuck with it for the entire song, whereas now I can step on a pedal and get that sound anytime and go right back to a 4-string sound when I no longer want it. It's not a total dead ringer but it's a lot closer than one might think.