|Boss OC-3 Super Octave Pedal|
1) It doesn't track well in a lot of the circumstances I use it, and
2) (This is the real deal breaker) Sound cuts out momentarily whenever the pedal is switched off and on.
Here's the demo video I put together for the OC-3:
I really do love the pedal, though, and from a practical standpoint its downsides aren't that bad. It's fun to play with and I would certainly recommend it to other people. I just honestly don't use the octave feature that much in my regular playing, and since it's not "everything I have ever wanted", I can't justify keeping it in my setup.
It has a sweet spot starting somewhere around the low G and extending up through the next octave to B or C. Under the G and above the B/C area its reliability starts to suffer a bit. Given, almost any octave pedal will have some trouble with tracking, but these things are good to know.
There are a few direct competitors, such as the Electro-Harmonix Micro POG, the Electro-Harmonix POG2, the Fulltone Ultimate Octave, the T-Rex Octavius Octave, and the Visual Sound V2 Series V2AF. In fact, there are even more octave pedals out there than that, and MXR makes one that sounds really great on Bass, by the way. However, if I was to purchase another octave pedal, I would probably be looking at the Micro POG and T-Rex Octavius myself.
Having heard the Micro POG in action before, I know it can be absolutely bone-crushing, even in dropped tunings and at loud volumes. The Octavius, on the other hand, has a really bright higher octave feature that I like. I wouldn't be inclined to turn it up super high like in some of the demo videos out there, but it could definitely add some thickness and top end to key parts in my songs. The low octave on the T-Rex seems to track really well, too.
Overall, I really do like the Boss OC-3, but there are definitely other options out there, so be sure to check them all out. Last but not least, it may be worth looking into a Boss OC-2 Octave pedal if you're interested in Boss's prior analog version.