The main selling point, at least as far as I read on these forums, is that fEarful cabs are very loud, and do not add any color to the signal sent to them.
That's all well and good, but I absolutely love the way my pair of GK410 NEO cabs color the tone of my 700rbII, and I love the way old Black Widow loaded Peavey 215d color the tone of my Eden E300T. I am told that a fEarful cab will get louder than my cabs, but honestly, I have never once been in a situation to where I have come close to maxing out the volume of the cabs I currently use. I'm sure they are awesome cabs, but I don't really have any desire to switch to a HI FI, PA style cab like a fEarful.