I would hardly say he's quicker than Mata. He's prob as fast as Rooney is now. Upgrade? Sure. Do we need him? No, he doesn't fit it any more than Mata. Even in his dribbling compilations, he doesn't use his pace to dribble past. It's more of a change of direction, then pass or shoot. Mata does that as well, but James is better. We don't need a wide playmaker, we need a winger.
He's more of a winger than Mata. But he's not Mane type player. He will score and create from the flank though. Of course, we have little idea what our formation will be next season. Or who is officially in charge. United have wanted James for a long time so I wouldn't be surprised if there was a bid