I've got 2 in my tank, with Pleco, Mollies, Guppies, Flying Fox, Cherry Barbs, Platy's and Swordtails.
Never had any problem with them, they always stay together, they even lay on the pleco, I've seen them chase things but not continuously, just enough to scare them off, never seen them being aggressive.
In my other tank I had 3, one of them got really big but even then they were fine.
They probably can and do get aggressive but I've never experienced it with them, and they're one of my fave fish.
My Mum and best friend have also got tanks with them in and no problems either.