The good thing about what Barkley did wrong in that video is that it can be ironed out relatively easily. In an EPL game those kind of errors are seriously rare, let alone two happening in the space of minutes, though. He just needs to be talked through matches by the old pros at first. He's got all the skill and more, but still he'd be a possible liability if played atm. We saw exactly that against Blackburn and this video shows he still has a bit to go on that front, which is frustrating, because you want a player with his talent in your XI from the off.
I'dd have reservations about starting him against United. Sub appearances at first is the way to go with the lad.