I have 2 trackballs (left & right), and the mirrored cursors let me easily distinguish between them.

It should detect the TrackPoint as soon as you move it, and the Settings box will change from Mouse1 to Mouse2. (That's what it does with my 2 trackballs.)

I've got a laptop with a 4K screen & touchpad (as Mouse1), and an external 1920x1200 as my right-side-extended desktop, with a USB mouse as Mouse2. I position the Mouse1 cursor mid-screen on the internal screen, likewise with Mouse2 on the external. When I move Mouse1, Mouse2 jumps to the far right ...