Well, it's nice to see that Sirius got a tiral, but it seems like Harry might have tipped his hand a bit too early. Showing that he could take over the ministry wards like that means that they will start trying to find a way to take that capability away from him. Also, he could have used his blackmail material on Crouch for other things, instead of burning it so soon. I'm unsure if there were advantages or not to keeping Crouch, but the way he did it seemed like a wasted opportunity.