Surprised no one's replied to this in one year. I have the Live 4 and think it's incredibly awesome and useful. Alone, the harmonies don't sound realistic. But mix them under your lead vocal and set the levels just right and absolutely no one could tell the difference. I sent an mp3 test to music friends when I first got it, saying "hey, what do you think of this song idea with harmony" and they said wow it sounds great... and never had any idea it was a harmonizer. When I told them, they're like "no way! It sounds like two different vocal takes."
I realize this might not help you, being a year late... but it's better to respond than to just ignore posts, as a lot of topics here go unanswered.
I'm thinking about picking up the Live 5, too and keeping the Live 4 for studio use.. the Live 5 is more rugged, better switches.. and is able to do A/B harmony parts on the fly... say, a 3rd up.. and then kick in a 5th when needed.
Definitely useful. Also, check out the Voicelive 2 by TC Helicon. Lots of YouTube demos on it... only a few with the Digitech.