true.. octavers such as the boss octave OC-2 or super octave OC-3, are pitchshifters that only do -1 or -2 octaves. because of this they are relatively cheaper (you can get an oc-2 2nd hand for ard $80-100).
its more for thickening up the guitar sound, make guitar sound like bass, or have a 50/50 blend to make it sound as if a guitar and bass is playing the exact same riff. or can use with a fuzz to get an octave fuzz effect. hehe.
pitchshifters like the boss ps-2 (check buy/sell section!), ps-3 and ps-5 do both octaves up and down. and they're more expensive.