Love the kole tangs! I had one for about 5 years. Wanted to start introducing new fish in the tank, and he was super aggressive. We had to give him to a LFS. He was attacking everything..!!!
I once had one....for about 2 years he was a ideal addition. Eye-catching....peaceful...helped maintain pest algaes....never caused a single problem in my aquarium. But....sadly it died shortly after switching from my old 55 display to a new 100 display. No obvious reason.......just died.
They can be a outstanding addition to a wide range of systems....and they are often mentioned as a good prospect for smaller aquariums (55 gal or so)...I have heard a few hobbyists mention problems with them but it seems to me the majority of comments have been very positive........