I've had lots of tone with icon warnings; most often valid, like when a slow moving car is turning off the road in front of me, but sometime just a radar reflection from a wheelie bin or other roadside object. It's especially startling on an empty road, when you think it's about to hit something you've missed - if this happened a lot I'd get it checked out.
It's only once hit the brake, when I was already doing the same thing but it beat me to it - as a white van man decided to emergency stop, he'd unexpectedly arrived at his delivery destination and couldn't see the
problem.
Overall my opinion is that it's a neat feature for every car to have now, especially if you are a pedestrian or cyclist. It will probably cause a lot of minor shunts and even some medium to serious car accidents on high speed roads - but unlikely to kill any of us as we're all in our cars.
If yours does trigger a crash it will still always be the person behind you's fault, as they should have left themselves reaction and braking time. Just blame it on HAL 9000.