I do a bit of BV in my bands and I've experimented with some of these pedals. They are really, really useful! I really liked the Boss VE-20 for some of its effects: harmoniser, megaphone effect, reverb... It did the lot. The problem for me came when the soundman just doesn't want to know: "woah woah woah it sounds like you've already got reverb and compression on your mic, No no no can't do that". I know, most musos would say the sound guy should just deal with what they're given, but I guess he had been bitten far too many times by weird kit turning up and misbehaving on stage. It made me really reticent to keep using it live, even though it added a great effect for certain songs and generally gave me more confidence in my BV.
So, if you go down this route of vocal effects pedals be prepared to tweak it so you can remove certain effects and give the sound guy the signal they want to make you sound good, or just bypass it and accept there isn't time or willingness on the part of the sound guy. If you are the sound guy, however, make sure you know the kit.