An Octave pedal does just that, plays an Octave (or 2) below, I'm not meaning to sound patronising at all here btw.
If you expect to play a low E and get a clean octave lower, you're kidding yourself. If you only mean you want to play a 'mid' E (7th fret A string etc), then you're fine, produces a real nice low E octave
Hope this helps in some way, the OC-2's really are great pedals, very musical effect, unlike others that may not glitch like they do, but don't quite sit in the mix as nice for me
Si