Adding a pot makes, imho, the travel much smoother (as the 'knob' has a longer travel than the little lever) and you can "see" where it is angled to when the P2 is at a distance - knob straight up = camera straight up etc etc . . .
Even though the slide switch works it is still not great. Mine worked for a few flights then had to open the transmitter and install a small washer so the lever end would make good enough contact to turn the pot. That was all it took to add the Potentiator Knob from Radio Shack. Simple process ( if you can solder a little ) and only like $7.00 for potentiator and the knob