Pros: great weighted club, easy to aim and set up.
Cons: You will know when you hit a bad shot.
Immediate feedback on swing is the best way to describe these irons. I am a mid handicap player and had tried a set of OS cavity backed irons from another manufacturer. Just did not like the way the weight was distributed and how most cavity backed irons looked when I set up over the ball. I purchased the S59 for everything they do that a cavity backed iron does not...beautiful setup at address, great weight distribution throughout the swing and the ability to move the ball around left or right with little brute force. Even though most people would find the fact that when you hit an off center shot with these you will know it immediately, I find that a great learning tool on the practice range. When you hit a good shot, it feels really smooth and effortless and the ball flight is amazing. I have found my practice time to be more productive with these irons and actually trying to work the ball with a fade or more draw has given my normal slight draw swing a relaxed motion that I can confidently repeat. It is like shooting pool with a golf ball, calling your shot and then attempting to do it. You will feel good about buying these when you have that one shot around a large oak and biting the green.
If you are ready to move up to a forged type iron, I would suggest you give these a try. Slightly more forgiving than many of the "low handicap" irons out there, but built with real quality. The Ping Pro wedges, new to the market, mimic these clubs in shaft and head set up. They are back-spinning marvels.