I think true SAEs are fine with Discus, it is the flying foxes or false SAEs that sometimes have issues with sucking slimecoat and aggression.
When I only had 1 SAE in my tank, I noticed he often chased my tetras (not the school, though, he'd just pick one at a time) all around the tank in a frenzy. When I got him 2 friends, however, this behavior stopped completely. The 3 of them hang out all the time and happily chase each other around. In fact, the first day I got the other 2, my first SAE was going crazy doing dances and playing in the bubbles of the air pumps for hours LOL. It was so cute and he had never done this in the several months we had him before we got his buddies. So I'd say they definitely do better, and are more fun and entertaining to watch, when they've got a couple of friends to play with.
When I only had 1 SAE in my tank, I noticed he often chased my tetras (not the school, though, he'd just pick one at a time) all around the tank in a frenzy. When I got him 2 friends, however, this behavior stopped completely. The 3 of them hang out all the time and happily chase each other around. In fact, the first day I got the other 2, my first SAE was going crazy doing dances and playing in the bubbles of the air pumps for hours LOL. It was so cute and he had never done this in the several months we had him before we got his buddies. So I'd say they definitely do better, and are more fun and entertaining to watch, when they've got a couple of friends to play with.