Disclaimer: I ride a substantial 4kW standing scooter with a real top speed of 100 kph / 60 mph.

Similarly to the unicycle stopping problem, panic stopping a Onewheel also doesn't seem possible without having room perpendicular to the direction of travel. I tried it in a demo arena but it didn't seem safe except for low speed travel on very large sidewalks* with space on all sides. Downtown streets seem too iffy to attempt, limiting its versatility. Unicycle-ish travel is great if you have the balance for and room to do it.

* Powered transportation generally shouldn't impede or compete with pedestrian traffic.