I never ever use the handbrake on autos, either older generation or new ebrake cars, except on extreme hills. The gearbox pawl is designed to hold the car and alone won't affect the gearbox life.
As an aside handbrakes are a poor way of securing a car as once brakes cool they often release and allow the car to roll. Equally on later generation auto release brakes each drive off takes a slice off the pads. XF handbrake users get trhough rear pads in 5k miles.
Finally in icy conditions handbrakes freeze on and either cables or pads won't release preventing drive off.
As an aside handbrakes are a poor way of securing a car as once brakes cool they often release and allow the car to roll. Equally on later generation auto release brakes each drive off takes a slice off the pads. XF handbrake users get trhough rear pads in 5k miles.
Finally in icy conditions handbrakes freeze on and either cables or pads won't release preventing drive off.