I mainly use this on projects I'm revisiting and mixing that were recorded 20 years ago or more and there's no hope if re-doing some shaky vox. Otherwise I wouldn't entertain the idea.
Anyway, it doesn't work miracles without evoking the 'cher effect', but with the right settings it can bring shaky things more in line, so we have something like 'character' rather than blatantly out of tune.
Put it another way, if you have an otherwise good vox performance with a few pitchy bits, this will work pretty well.
I tend to use the two main knobs in a kind of middle setting, so it's slightly less sensitive and corrects more slowly, which sounds more natural.
Also it's essential to pick the right key to work in. So, if you're working on something quite proggy with more shifts in key perhaps, then you'll need a version with more features. There are ways round this in the DAW of course though with a bit of creativity.