1. As far as rules, they aren't street legal. They are considered toys.
2. You'd get better use out of a moped or a bicycle.
3. They are tricky to ride and plenty of people hurt themselves on them.
4. They are too small to be a legit form of transportation without looking like an idiot.
5. Again, they are toys. No sane person should ever want one of these.
6. The cheaper ones are made in China and WILL break. I hope you know how to do small engine repairs.