Update: Got a picture of a young rider today--no helmet.
Been seeing these a lot of places around. I've only seen three people riding them--all in their late teens or early twenties. I don't think any of them had a helmet on. Seems cool for that age group, though not for older people. And not useful for shopping or people with kids.
An Oregonian review answers some major questions like speed (15 mph), balance and safety issues (not the best).
Be interesting to see how they do here.