Deeper centre of gravity in longer irons for easier launch; further forward in short irons for control. Variable cavity thickness allows more weight behind centre of clubface for a solid feel.
A clean look at address but not the most attractive rear view. They felt gorgeous out of the middle and were the longest here. Noticeably different feel on mis-hits but even they flew in the desired direction with a decent flight. The heads are very small, they don't feel as if they'll forgive any off-centre strikes.