I switched to Look from Shimano years ago for the simple fact that the float in Look allows the toe to pivot more than Shimano, which tend to hold the toe stationary and allow only the heel to pivot. A finicky left knee forced the change, and my knee is happier now. Though Look boasts of a larger contact area now over the previous Keo, I honestly cannot feel a difference. But where I do notice a significant improvement is how the pedal hangs when not clipped in. With my old Keos a no look clip-in was a hit-or-miss affair, whereas with the latest version it's a hit nearly every time. That's important because it may save you some embarrassment occasionally or possibly some bruises if you ever get caught on a steep uphill and need to clip in quickly.
I normally use Look but only their less expensive. This product is used on my triathlon racing bike and I love them.