I don't know exactly how a harmonizer works, but it's hard to fit it perfectly because in some solos you will have major and minor chords, which would make the harmonizer sound off the scale being used over the current chord, a good example of it is the lead guitar part right after Bat Country's solo, Syn uses the harmonizer while Zacky is playing rythm, there is one note that will always sound off compared to the studio version, but it works perfectly on "This Means War" intro.
Again, I have almost zero theoretical knowledge about this but I just noticed it, still a very fun effect to use