Removing the magnet on the KEM does improve the feel of the scroll ring, and it is usable. But in the end, it could have been a better implemented design.
The need for a wrist rest is a minus too. Overall, it still is a fine trackball.
The kensington slimblade takes the 4 button trackball to a new level, imho. The scrolling is incredibly smooth, the little ruby tips the ball rolls on are embedded in the housing and you don't need a wrist rest.