Another thing to consider before buying any vocal processor is the wide variety of harmony types that are possible. Audio activated devices generally produce chordal harmonies. But there are many other kinds of harmonies. (several varieties of scalic, note driven etc)

If you want specific notes (such as the harmony used in Scarboro Fair) a chordal harmony won't do that. It will provide a theoretically correct harmony, but it won't be the one in the original song. If you are into note-for-note reproduction of cover songs, you definitely want to look at a programmable device.

A programmable device is capable of reproducing ANY harmony that is possible (If you are willing to endure the learning curve and time to reprogram your set list of songs)

The chord-based harmonizers do one thing very well: they provide excellent sounding backing vocals that fit a given song in a generic way (much like BIAB reproduces songs very well, but without the signature licks)

https://www.dropbox.com/sh/ey71h8ep047758h/AAC12jNM0Hz9Q8zsh5iDeqNHa?dl=0