I read through that page and it doesn't seem to explain how it actually works. With only one roller how do you move the mouse up and down, left and right?

I was confused at first but I realized I was looking at the scroll wheel surrounded by mouse buttons. Cursor movement is done with the "bar" above the buttons/scroll wheel. Move left/right in a finite lateral motion or up/down in an infinite scroll motion.

You roll the roller for up/down, move it left/right for ... wait for it ... left/right :)

It's really intuitive.

What happens when you reach e.g. the rightmost position of the rod?

A mouse has "infinite" movement, the rod only has infinite vertical movementent, unless I'm missing something.

There's a "button" on the end of the rod. If you slide the pipe fully over and depress the button, your mouse will continue to travel horizontally.

Imagine a long rod. Slide a shorter pipe onto it. You move on the X-axis by sliding the pipe left/right on the rod. Move on the Y-axis by rolling the pipe. Click by pushing the entire contraption down.

Yeah, the RollerMouse is awesome. Turned out not to be a good solution for me, but I had no trouble operating it.

My wife uses one of these, and it has completely eliminated her RSI. Great product.