In my experience they can be a great tool, but the kind of thing you want to use sparingly.
When you bump up the lows and highs, they can sound good if you're into that type of thing, but sounding too scooped can make the tracks sound terribly drowned out in a mix, and I found the sound going into a microphone when micing up a cabinet or something with a BBE on, wasn't as good and didn't translate as well. They seem like they could be fun for live use though maybe.
I've never used it for vocals but I imagine you would be able to get some good sounds and clarity with it.