I have two right now and they're not aggressive at all. I've kept them with anything from small tetras to adult severums, dempseys and snooks over the course of the three years i've had them. They pretty much stay in their own area and don't even mess with other catfish (I've kept them with full grown raphaels and 6" synos as well as smaller species).
Mine definitely seem happier with a school, I'm currently looking to replace the two that I've lost.