Since my first encounter with a harmonizer, I've been wondering what on earth I could use it for in my own music. The added tones always sounded strange (unless rocketed through a fat distortion) and seemed a challenge to use without creating a cliché solo sound, let alone using it for clean purposes.
But then this unit came along. It's lovely: clean, overdriven, however you like it - but it wants very clean power. I recommend a Boss PSA 230S. Also, make it the first pedal in your chain, before a compressor, booster etc. It works best with a direct guitar signal. If not, it will produce rumble and clicks, probably because it's confused :-)
The poly feature isn't great, but for single tones this harmonizer is the best ever... and cheap, by the way. It's superfast, and its added tones easily match my strat's different pickup signals, and pitch bending, vibrato, slides, tapping... Now I find myself wondering WHERE I can use this harmonizer on the new album.