I got yelled at in Copenhagen for not knowing about this and trying to slow down and look for a gap in traffic to turn left.
I looked up how to do it after that but the idea of getting flattened by a car turning right during my hook turn always scared me and made me think it wasn't a great system.
Can't see how the getting flattened could happen tbh. You get the jump at lights, and any driver having the temerity to get too close to a cyclist, let alone flatten them, will be roundly abused, or worse, by every cyclist within a 50m radius, and that is a lot of cyclists. (I remember watching a mum kick an open car door closed, denting it, because chummy had parked in the cycle lane. She was cheered.)
I found if you complied with the rules of the road and behaved predictable everyone was happy.
If you failed to comply or behaved unpredictably then you got pinged at, yelled at, honked at and everyone, even bystanders would castigate you
But... if you flouted the rules egregiously and rode courier-style then so long as you didn't inconvenience or endanger anyone else no one would say a dicky bird.