Except that in my experience, they do get more aggressive and actve as they get larger. That was the point of my original post. They were attacking adult discus and severums in my large community tanks, to the point that I had to remove them. They made my other fish skittish and uneasy.
I think it's important to hear various personal accounts so that people can make an informed decision. Maybe others have not had that experience with festivums, but it was the same for all three groups of mine. Any time I see a question about Mesonauta, I always weigh in to let people know what they may experience.
I've never heard of them becoming aggressive like that; good to know, I guess.