I've used it with perfect success many times now. It's really useful for parallel parking in a jiffy, if it's a busy road.
I keep it as a shortcut on the homescreen so it's quickly available.
You press the button and drive along, the car scans for open spaces, and you get the option to press "Start" once you pass an open space. If there is no room for a parallel park, it will give you the option of perpendicular instead.
Turn your mirror adjustment knob to left (if you have RHD) and the mirror will dip down when reversing and show you the curb. Use this as a gauge.