CADad- That's one thing I've noticed as well. He also has an uncanny ability to stay very linear towards home plate, which I think is unusual for a person with his size and his mechanics.
His arm action scares me a bit to be honest. The timing mechanism that he (and many other Japanese pitchers) use by pausing at the top of the balance point could potentially create a slight arm drag. His wrist tuck (similar to Bruce Sutter) and ensuing angle of his front side/glove, IMO, could result in excess torque on the elbow. At the time his landing foot touches the ground, his arm slot is eerily similar to that of Mark Prior and Kerry Wood.
Just some observation...that could very well be way off base. He is obviously incredibly talented nonetheless.