[Williams]

It’s safe until it breaks and grandma tumbles down the stairs with a piece if machinery on her back.

[pepsi_junkie]

It's true that more complexity = more ways and opportunities for a system to fail. But then again grandma could roll backwards down a ramp too.

Anyway the stairs thing looks like mostly a gimmick though and all the examples I've seen have a person leading the chair pulling it to stabilize it. It's not autonomous. The real use case is allowing it to safely go over uneven ground, curbs (one small stair, essentially) and elevate to eye level of standing people.