I have a Flagtail, a Festivum, and six Chalceus in my Eartheater tank - I must like top-dwellers!
My Flagtail has never bothered anyone, but I have definitely heard stories of them rasping on large, slow-moving fish.
A lot of people have said that Festivums are not top-water fish, but mine spends most of his time in the top 6" of the tank.
The Chalceus are some of my favorites. I haven't had any aggression issues, but they are very skittish and tend to flip out if you startle them. They definitely need a very tight lid - I lost one that jumped out through an opening for a HOB that was only about an inch or less wide. Chalceus are definitely the most top-oriented by far, they never leave the surface of the tank.