Nike has changed the performance of the Nike Slingshot 4D irons in four critical areas. Nike positioned the weight differently in the long irons than they have in the short irons in order to get the ball flight you want in each club. Nike also made the long irons wider, similar to the hybrids, to get those high soft landing, and they made the short irons thinner so you can control the clubs making more accurate shots at the pin.
Another change is the offset in each club, making more offset in the long irons and decreasing them as you went down to your short irons. It does help you square the club head in the long irons and prevent those pulls in the short irons. The long irons offer more forgiveness and launch the ball like a hybrid, and the short irons are more accurate because of the profile of the club head.
You can get these Slingshot irons in graphite or steel for about $400, as of 2009.