I've been looking for a smart harmonizer for some years. Firstly I wanted the Boss PS6 but I also needed a pedal to virtually change my tuning, so I ended buying a Whammy DT and thinking that I could use the minor/Major 3rd mode to do some harmonies. Well, I couldn't, moving the pedal each note to harmonize a phrase was not a very intuitive way of playing and, besides, having the harmony in front of distortion didn't sound that good to me.
I came back to my Boss PS6 pursue, but I tried it twice on a store and couldn't like it. And then it happen... I found the quintessence randomly in Thomann's catalog and I couldn't believe what I read and heard in some demos.
I never tried the high end harmonizers, but it is hard to believe that they can track better than this one. Soundwise it does a convincing imitation of a second guitarist, except if the harmony is an octave up, for some reason it sounds a little artificial to me. I prefer using this pedal in the FX loop, it sounds better with distortion than in front of the amp. With mash and the editor I believe that this pedal can do really amazing things, making a smart harmonizer even mor flexible. Unfortunately the TonePrint app isn't very compatible with Voiceover to do some advanced configurations so I couldn't try it.
To summarize: this pedal doesn't replace having another guitarist, or recording two different guitars, or even harmonizing using a delay pedal, but for an instant harmony partner it can't be beaten, the tracking is flawless (except when playing more than one note at the time), the mix setting really helps to make it as prominent or discreet as needed and the possibilities are endless! I really like the fact that, if using an harmony below the original note, it can be fooled to harmonize a harmonic minor passage!