in my experience with pitch shifters and octavers, I have yet to find one that sounds natural... and the lower you drop, the more unnatural it sounds. I wouldn't use it in place of having to retune, but I suppose that you could if you need to, such as you have half the song in drop D and the other half in drop C or something like that... an octaver drops you one octave, which is 12 half-steps, making your guitar sound more like a bass. and a pitch shifter will raise and lower you only a few half steps at a time.