When using bafang motors 500-1000watts, it is quite important to have these sensors to cut the motor power the moment you apply the brake lever. Without them, the motor only stops 0.5sec after the rider stops pedaling. This 0.5s delay may cost a lot in emergency.
We prefer install one on the left lever if you are right handed because these sensors often move around causing motor power gets cut out randomly and having two just increases the odds.
VOLT EBIKE AUSTRALIA