I just spent about 45 minutes using the Green Brick this morning on two carbon steel knives that I have: a carbon steel Dexter Chinese Cleaver and my Kanehisa carbon steel 240 yanagiba. I then used it again on my Global G-2 and Sakai Takayuki Inox 120 petty.
I can't recommend this stone unless you're primarily sharpening softer stainless steels. All of the feel that I like with carbon steel knives is lost on this stone. It feels less like a stone and more like putty. The feedback and feel are worse than I remembered.
It provides a decent edge, a relatively nice polish on carbon steel knives, but it dishes and gouges super easy, and for that reason, it's very difficult to sharpen the tip of a knife without gouging the stone. If you sharpen sectionally with perpendicular strokes with the knife nearly horizontal and the stone vertical, it's ok; if you use any kind of sweeping motion, or angle your knife in any manner, you will probably gouge the stone. You'll have to be very careful if you sharpen a heavier knife on this, IMHO, because of the weight of larger knives. In addition, it loads up my Atoma 140 like crazy when flattening.
But, for softer stainless, it provides a good edge, and decent polish more than other stones that I've used, bad feel and feedback aside.