Not only is this a parking brake, but it only activates the rear brakes. The front brakes do most of the stopping (about 70%) in normal use. So don’t expect it to work as well as all four brakes together.
I would pull the parking brake in an emergency where the normal brakes fail, but since they only work on the rear axle, stopping distance would be signifigantly increased. In a true emergency, you should also downshift, even if you are driving an automatic.
Keeping your car stationary is far easier than stopping it. Don’t judge the effectiveness of your parking brake in this manner. Besides, when parked on a hill, the transmission should provide extra insurance, since it will either be in park (automatic) or in gear (manual), right?