I play both bass and lead guitar, but since I can't really do both at the same time, I use the Octoplus to mimic a bass during parts of my songs where the bass would normally follow the lead guitar. To do this, I run the clean signal from my guitar (Jackson or Hamer with humbuckers) to a Morley ABY. The A output goes to my standard guitar effects and amp, while the B channel goes to the Octoplus and then a Randall RB-60 bass combo. So I'm not really using this so much for an octaved guitar sound as I am for a "phantom bassist". I've only worked with it at home so far, but it does what I need it to do and will be using it live most likely.
Since I am running the Octoplus straight to a bass amp, I max the Octave Level, zero the Direct Level (don't want the sound of a clean guitar) and adjust the tone as needed. No noise to speak of, since there's really nothing much to dirty up the signal. The tracking is, for better or worse, about what I expected, with chords sounding horrible and tracking getting thrown off if I bend a string or hit the low E very hard. If I was trying to nail a real bass tone, it wouldn't really cut it, but for doubling a lead guitar track with a psuedo-bass sound, it works just fine. The only issue (aside from the tracking) is that the pedal's signal seems a bit weak when the Direct Level is turned all the way down, ie. only the effected sound is heard through the amp. It's not going to achieve a strong, punchy bass tone, but again, the signal is coming from a guitar humbucker with light strings, so I feel that a score of 7 is pretty fair.
Here is where DOD products can be a problem. Having only had this pedal long enough to experiment with it at home, I can't say how it would perform under gigging conditions. I bought it used, and already see that the pedal switch itself has potential for problems -- it sometimes responds with a light tap, but other times really needs a hard stomp. I won't rate this at the moment, but I will remain wary of footswitch problems down the road.
I play thrash and melodic death metal. My band doesn't currently have a bassist, but since I played bass in the studio, I know which parts really require a bass sound. The Octoplus will do what I need to do, although I wouldn't say that it's especially phenomenal in terms of sound or construction quality. However, there are so few octave pedals that get consistently good reviews, and so few available to even try out in my area, that I figured it was worth $30 to mess around with it. It will help me fill a gap in my band's live sound until we find a better solution, and for the price, I am happy with it so far.