If there is not much traffic, you are right, but this is China.
In case of speeding across intersection on red light, the guy doing it will probably have caught with the rest of the scooters by the time cop gets to it.
Then there is siren, and nobody in that crowd of scooters will know who it is for (except perhaps that one violator).
"Best" case scenario is that they all start to try pulling over in limited space, and that won't be pretty.
Likely scenario is that at least some will (for whatever reason) ignore the siren, and not do that, and hit the others trying to find space to pull over. Some will no doubt take pulling over seriously enough to pull over to pedestrian lane, because there will not be space to go anywhere else.
And often there are cars around too. Will they know the siren is for scooters and not them?
I can imagine quite a chaos because of one scooter.