Kole are from the genus ctenochaetus and have brushes for teeth, and differ from zebrasomas and acanthurus which have the normal pointier mouth. Because of this main difference, ctenochaetus can't bite off anything. So if you have calurpa leaf, he can't eat it like another tang, but can only graze off the surface of the leaf and since the leaf moves around, he doesn't quite get in contact with it. He can eat off any other solid surface and is great at preventing hair algae buildup, but once it gets beyond a certain bushiness, he can't eat it anymore. Since his mouth is so bulbus, he is also no good at getting into the fine spaces. Ctenochaetus are as much as a denitris feeder as they are algae grazers.
Also, I noticed a major difference in how koles fight as compared to the other genus, in addition to the usual try and slash him with his claudal spike, they also bite each other on the side, which cause this terrible rash like wound, since they scrape off the skin.
Summary - you can have a tank full of tangs, but only one ctenochaetus.
They are really hardy, I keep one in my main tank, and one in my calurpa filled refugium.