It's not so much the brakes being stable, it's the operator's body with its c.g. 1m above the board. A maximum deceleration for tires on a good road is generally 0.6-0.8G. So in order to avoid being (literally) thrown off the board the rider needs to be
leaning backwards by 30-40 degrees
before applying the brakes.
There's no equivalent to this behavior in any other vehicle. In a car you just hit the pedal, on a bike you just squeeze the handles and hold on, on a seque (the closest equivalent I can think of) you must lean back to actuate the stopping.
On a long board at 20mph if you "hit the brakes" you crash, period. That just doesn't sound equivalently safe to me.
