The problem is that the way these are designed, there is a ton of friction. If you remove the upper part of the shell and lube the moving parts a bit, it works much better, but you'll have a lot of backspin. I had to break out every other tooth on the optical encoder wheel, which helps reduce the backspin at the expense of sensitivity... but I still ended up not installing it in my panel.
I'll probably buy the $25 arcade trackball from Wico and hack it to the board of this trackball.
--Chris