These are much safer than small-wheeled scooters as their larger wheels allows them to more gracefully handle bumps in the road.
Also, unlike most ebikes I can actually sit stationary on these without falling over. I'm very short and most ebikes are not designed for short people.
Yeah rental ebikes don't scale down very well. You should be able to buy a bike that fits you well, and add ebike capabilities via a kit (yourself or have someone do it).
I haven't used a balancing unicycle, but based on experience with other balancing vehicles, I doubt I'd feel safe going as fast as on a scooter. Sounds like you might own one?
Also, unlike most ebikes I can actually sit stationary on these without falling over. I'm very short and most ebikes are not designed for short people.