Try it before making claims like it's "horrid". With the right trackball, it can work very well. I've used the Logitech Trackman (that's the ambidextrous model, not the right-handed thumb ball model: that does suck) for many years.

Thumb is left click, and I don't know about you, but that opposable thumb is a pretty fast digit, index finger is ball, middle finger is brake (keeps ball movement from overshooting), ring finger is right click.

The claim that this limits distance is a canard; if you can't slew the entire screen in a single index finger movement, the fault is not in the trackball but in the setup.

Used to have a Kensington "Expert Mouse" trackball. Didn't like it as much as the Logitech. It doesn't conform to my hand.

Trackballs embedded in a keyboard or gamepad are worthless. It's got to fit your hand as well as a good mouse does.

I used one of these to play Left 4 Dead 2 and System Shock 2. Other than those two games, I've mostly been playing RPGs. I seem to be able to play anything with it. It did take a little while to get used to it, and I wish they still made the wired version of that trackball.

Due to wrist and hands cramping after 5 minutes of use with a standard mouse, that trackball is all I use now besides occasional use of my laptops trackpad.

Yeah, the same I have (M570), I probably discussed about it with you before.

It is definitely not a horrible experience like some make it to be (maybe they are talking about the "on top" trackballs, not a thumb-trackball?), but still, in high speed FPS games, I prefer a mouse. So unless there is some reason not to use a mouse (e.g. no table, or wrist problems), to me mouse is still preferred overall. Mouse is also much cheaper, the M570 is kinda pricey.

But as said, I don't regret buying my M570, and I do use it quite often, whenever I use the PC on the sofa (without reaching to sofa table). Except for the high-speed FPS games, I don't really miss a real mouse at all. Since I have both the wireless M570 trackball and a wireless mouse connected all the time, I can switch between them on a whim.