5. Shaw is still extremely young
Imagine what you were doing when you were 18. Well Shaw became the youngest Southampton player to start in the Premier League, is now the most expensive defender in British history, and has featured for England in the World Cup.
If Shaw can continue his amazing rise to stardom at Manchester United, then the Red Devils will have a world-class left back that can occupy the position for a generation.
Some critics and former players have even praised him as to being better than Gareth Bale, and if so, would mean that £30million would be just 1/3 of his value in the future.