I used one. Not much to say about it.
Construction is flawless as always with Catalinbread.
It boosts in Boost mode. Fat brings too much medium range in the tone, too boomy to my taste.
I don't know for sure. I'm at work right now on a computer that doesn't have Flash, so I can't check the website again. From what I remember, though, it said it adds some warmth and grind...? So it may be something of a bass/low mid boost?