It’s legal and a cultural norm. I have mixed feelings about it. More dangerous, but saves time on the freeways.
All about saving time…
Inside mirror, depending on intended turn right side mirror left side mirror, left side right side mirror, then turn your head.
All blind spots should be covered.
When a gap is available move your car all the way to the sidewalk and indicate where you are going.
The car behind you going straight should leave a gap and all the scooters should move over to the left. Much faster saves a lot of time.