A lot of the time our 3rd string qb has had all the tools but that is it. They end up having to learn how to be a pro QB but never end up getting there. Reading defences, accuracy, putting a nice touch on the ball, making good decisions, throwing the receivers open... Those are all things good QBs do.
McGuire seems to not only have the tools but possesses some of those traits.
Now like Ripper mentioned, it's about getting to backup QB for next year.