that would be me.....
I mentioned they eat sponge, they also are algae grazers and as you read they are not particularly reefsafe. However the biggest issue w/ Moorish idols are they do poorly in the home aquarium, for whatever reason. There are a number of stories recently that folks have been able to keep them 1 yr or more- but this is the expection not the rule. Maybe we are getting better at keeping them, or maybe collection & shipping are better- i dont know for sure. But I see them every week in Houston at our LFS, and thet usually get sold, bu i almost never read on our local webboards- bragging about their moorish idol success. Feel free to check RC as well. Also if you get a really young one, they tend to do better and eat a wide variety of foods.
I'm not going to dissuade you from keeping one-- just be aware that they dont have a great history of success in the home aquarium