I have one and use it regularly. The overdrive is definitely different than any others you have heard. Not a Tubescreamer clone, not a Blues Driver, Fulldrive, etc. super-transparent drive, and not really heavy. It's its own thing. I think it sounds fairly thick, lets your guitar tone come through a bit, but not a ton, still has dynamics, and can get a bit of a fuzz-type tone with the right manipulation of the knobs. It is a bit of a darker overdrive, but if you crank the tone knob, you get a ton of treble, but its still got the dark twinge to it.
It does take a bit of playing with to get the drive to sound just right, but when you do, it sounds amazing! Holdsworth uses it, so it can't be that bad.
O, and the boost is great!