To try to make the effect of the difference clear:
The "r" in both throttles means it is radio-equipped, so does not need to be plugged into the panel to control locomotives.
The Cab06r has an encoder that moves when you turn the knob. (It could have been called the Cab06er.) When it moves clockwise, it sends a DCC command to speed up, and when it turns counter clockwise, it sends a command to slow down. The knob will continue to turn without reaching a stop, even though the loco has completely stopped or reached maximum speed. The advantage to this type of encoder control is that you can switch between locomotives that are running without affecting their speed until the knob moves.
The Cab06pr has a potentiometer that is turned by the knob. It adjusts the loco speed from 0% to 100% according to where the knob is positioned between two stops to its rotation. 0% off the counterclockwise stop to 100% of its travel to the clockwise stop corresponds to loco stopped to loco at full speed. If you switch between two locomotives that are running, the locomotive that is newly addressed will change speed to whatever the potentiometer is set to. Because you may want to switch control between two locomotives that are both running at the same time but at different speeds, this tends to make it difficult to not make a noticeable speed change in the locomotive that you switch to.
