There's not a lot I can add really that
@captain nemo1701 hasn't already said. Post of that day there I think.
If you go to any of the cities where these are common, they can be a complete and utter menace because they're a boon to the terminally idle. Sadly the terminally idle do also tend to be irresponsible and selfish people. Hire versions are casually tossed (sometimes in little tangled heaps of 3) in the middle of city centre pavements, riders ride them wherever they damn well please at silly speeds (including pedestrianised streets, parks, roads, cycleways, veering between any or all of them as it suits), with associated increases in injuries and hospital admissions. Many city mayors are trying to ban them now.
I think the theory of the machine itself is excellent, and it would be the ideal transport for some (including my Mrs who works one town over, in an isolated part of it). I do think most cyclists would ride them responsibly. The trouble is that there are a lot of irresponsible people out there. Paris, Brussels, Atlanta, and dozens of other cities have already found that out.