I vote “failure”. In a practical sense they fell far short of changing the way we move around.
I actually saw one this past week, in the very long indoor walkway that ties together a local hospital and buildings of medical offices. It came up behind me and made a log of whirring noise, and I expected to be passed by a golf cart sort of multi person conveyance, so its noisiness for a single person transport surprised me. My first reaction was, “Oh yeah, I remember those!”