I know nothing about Aguero, but I'm going to say for now, based solely on a WAG, that he's a reliever, throws hard, has command issues, and is a converted outfielder.
I will now go look up Aguero, and update this once I figure out who he is and what he does.
UPDATE -- Here is Aguero's B-R page. He is a reliever, he appears to have command issues, but he's not a converted outfielder.
Not sure what the story on his fastball is.