This seems to be a reasonable regulation. They should be allowed on designated bike trails only, and even there should be subject to a speed limit of ca. 18-20 MPH. They also should be the kind that provide assistance only when the rider is pedaling, as this gives them some feeling of how to slow down or brake if necessary. A vehicle that provides power independent of pedaling action is much more dangerous, as it removes the connection between motion and effort, and turns it into something like a moped. No electric scooters or electric skateboards should be allowed for that same reason.