I don't know if your Endura Pro was USB or PS/2, but I have used two Unicomp Model Ms with trackballs built in and the trackball performance was unacceptable fo

I don't know if your Endura Pro was USB or PS/2, but I have used two Unicomp Model Ms with trackballs built in and the trackball performance was unacceptable for the USB model and excellent for the PS/2 model. Seems silly, but I think their USB firmware is probably a poor hack. The trackball in the top right corner combined with the Model M form factor was an unknown dream realized when I was using it regularly, so while your opinion is as legitimate as any I have to disagree.