Imagine losing your balance and falling off. With guard rails and fully enclosed rotor blades, it might've worked. I can't think of anywhere to deploy it where it would have advantages over other modes of transportation. Desert, coastlines, ... but then what for? Landmine detection? It's also really loud, so no public or residential deployment. And even if it had been hardened and dummy proofed, disruption of the bla…
> Imagine losing your balance and falling off.
Or a sudden dog running across the field. Or checking your insta-feed and overlooking that group at the wedding crossing the park.