#2
The Super Octave only lowers the pitch coming from your guitar (I think)
It's the Super Shifter that does harmonies.
Axe FX 2
Matrix GT1000FX
Mesa 4x12
Behringer FCB1010
#3
Yes.

The octave pedal is aptly named because it creates octaves below the guitar signal and mixes with it.

The super shifter creates pitches (other than octaves) that harmonize with your guitar signal based on what you set it on.

It doesn't get any more simple than that.