The biggest concern I have is not with the playing side, tbh, it's with the shadow he'll cast over the rest of the team.
He is a global superstar. Not a superstar player for a long time, but a super star in terms of image. We are in the media's eyes from this point forward now Rooney FC.
Not that he has an ego that he needs stroking or anything, he's very collegiate by nature. But I have a lot of reservations over how team-mates handle this type of immediate downgrading in their own importance. You need players who feel they can be leaders of the team. With Rooney in there it's impossible.
We'll see. For now, and on balance, it's a welcome development.