I have Diamond Brite and it's as smooth as can be; at least as smooth as plaster. You will probably get some mottling in the finish if you use one of the darker colors, even if the plasterers do a good job and follow SGM's finishing instructions (which mine did not). If you do go with it, make sure the plasterers are aware of those instructions (link below; they can water wash, acid wash, or high-acid startup).

Mine is French Gray and has some mottling, but it seems to be evening out (6 months new).

Diamond Brite application instructions: http://sgm.cc/download/installationm...amondBrite.pdf