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I saw a guy in Brighton having one of these confiscated by the police. He used to tear around the road and cycle lanes wearing a full face helmet at 35+ mph. I'm sure i saw in local paper he was fined as well. Local police are pretty much turning a blind eye to whatever people are up to on their E-scooters but this guy got his collar felt. I expect that to be the same in any other city.
EDIT: i found the report in the local paper. Police are classifying these as mopeds not E-bikes so compulsory helmets on roads only and not even allowed in cycle lanes
There's plenty of footage of people on those being absolute menaces at trail centres. They look like great fun, but unfortunately I think they're in that unfortunate middle ground of being illegal just about everywhere.