No, you do NOT need an additional 'mechanical switch'.

It even describes this in the instructions.

The transmitter on, the switch on transmitter on, you're ready to run.

The switch off on the transmitter off, you're ignition is OFF.

BUT BUT BUT, with this method, they suggest disconnecting from Batt source between flying days, as the
unit will continue to draw a LITTLE bit from the Rx pack even when not in the 'on' mode.

Good luck !

Steve Beach
Team LIMAC !