Why two Joysticks
The Joysticks can be mounted wherever you like with the provided epoxy putty.
The typical positions are on the shifter, or the emergency brake. When driving , and going through the gears, having a joystick at your fingertips allows you to add assist or regen as you like with the same hand that is operating the shifter.
Once cruising on the highway, having your arm stretched out to the shifter in 5th is not comfortable.
The e-brake position allows you to let your arm hang comfortably at your side, and operate the joystick there for a more comfortable adjustments right at your fingertips.
Some of the other ways people have installed the sticks are shown here: