I've watched quite a lot of him this season for Wigan and not been at all impressed. He was decent in a couple of the early games, but it's gone downhill from there. Almost seems to have taken a step or two backwards. That probably has a lot to do with the fact that he's almost always playing as a centre-forward. He struggles to get any kind of touch going unless he sees plenty of the ball, which isn't going to happen playing up front for Wigan at the moment.
He's a quality player, and eventually he'll get the opportunity to show it, and I'm sure he'll have a good career. But I don't hold high hopes of him making it at United. Not very mobile, and not quick-thinking enough in my opinion.