"Selim Bradley" is just a shell. The boy himself is completely hollow inside - a container, if you will, allowing Pride to pass as a human. He's the oldest Homunculus, wielding some rather dangerous powers in his true form; I've worked with him myself, and I've seen what he's capable of.

Assuming that the Homunculi are bound to the same rules as alchemists and can't access their powers, he shouldn't be much of a threat; at the same time, I would be careful with what you say around him.