We have them here on trial basis too. They are left all over the place by users. Then collected sometime late evening, then reappear early morning, parked on pavement corners in groups of 4 to 6.
There have been a few close calls with pedestrians, cycles, motorbikes and cars. More luck than judgement there's been no direct collision or injury.
Maybe they do have a place, but given that cyclists, skateboarders and skaters are strongly advised to wear PPE, and government spends millions on advertising this then personally I think its remiss that the hire companies involved are not forced to provided appropriate PPE.
I Understand that makes the hire and go a problem, but it needs to be given some thought.
It won't be long before one is in a serious accident, and it will have lawyers all over it for compensation for injury against the hire company, for failure to take reasonable action to protect the hirer's.
Make great sense for city centres to reduce poor air quality, as they can easily set up road and cycle lanes to accommodate them. But in outlying residential areas they could become a menace.
So generally its a good idea, but the implementation has not been thoroughly thought through IMHO.