The Segway had a shorter platform, so the user wouldn't put it as far out of balance under typical use, and it had handlebars which allowed the user to pull it back if they started losing their balance. It also had a lower top speed of 10 mph (12.5 on later models); the Onewheel could run at 15-20+ mph.

(I use the past tense because Segway production ended in 2020.)

I think the pole in the center prevents your body from leaning forward more than the Segway will tilt (i.e. it can just tilt backwards, and push your body back where it belongs).

With the Onewheel you can just lean forward as much as you like, and the board is supposed to accelerate to bring your center of balance back into the middle.

Yes, they were recalled because of it.

https://www.cnet.com/tech/tech-industry/injury-risk-prompts-...

All self-balancing vehicles have the same failure mode -- that you can exceed their ability to catch you by leaning too far forwards.

The Segway benefits from having a big pole it can jab the rider with to make them learn back. But it's entirely possible to nosedive one if you try hard enough.