If you've got a decent training regime with nice facilities, he can turn out as a true quality player. I personally prefer to train him as a Forward, rather than a Winger, simply because he has higher fundamentals for the striker position to begin with. He lacks crossing ability, but has an ok finishing ability, and his speed/flair will cause havoc in the box.
He is worth 20mill if you plan to utilize him as a long term player. He will end up worth more than that provided he's trained well. If you're looking to the short term, maybe look for someone who is more accomplished at the moment.