The thumb trackballs are on bearings with higher static friction than the logitech thumb balls. You get used to it, but immediately feel the difference if you go back to a logitech. The buttons are great though, I remapped the middle-click away from the track wheel because with the 4-way wheel it's much harder to middle click, since my elecom has 3 non-scrollwheel buttons it still works great.

There's a forthcoming linux kernel fix to get the right button to work on the EX-G models.