The club is designed to have more head weight behind the sweet spot, and being that I am not a long ball hitter, I have picked up almost 10 yards per iron. In conjunction with the relocated mass behind the sweet spot, Mizuno uses something they call "Hollow Technology" to leave a hollow pocket in the iron head, I am not sure of the mechanics behind this pocket, but I like it.
The MX-11's swing straiter and smoother than any other club, I have gained quite a bit more accurcy and I can hit the lower irons (3 & 4) without cursing at my club after I swing. These clubs also look great in the bag, I have receive alot of compliments on the clubs. I also am very fond of the grips, I could tell my old set were spinning in my hand, I feel like I have more control over these irons, results, more strait shots, less rough.
I have honestly not found any comuplaints, especially if you can find these for under 500 bucks.
The Mizuno is a well designed club. I originally went to pick up a set of clubs that I would work through and replace with a better (more expensive) set someday. Now I am not that sure I will need to. The MX-11's have not let me down yet.