This is a great contract. More for the Jets than Rex, but it certainly doesn't hurt him. If he can do what he believes he is capable of, he gets paid. If he can't, the team gets out of it early.
The way it's structured, if he hasn't shown enough to warrant another extension in 2015, he'll never get to the point of a "lame duck" conversation again.
This is a great deal for everyone involved. It removes the dumb distractions and lets the team get down to the business of building a contender.