After first refusing, OneWheel recalls all of its self-balancing electric skateboards

That's not entirely true. The "top speed" on these can easily be exceeded although the board will attempt to thwart this by changing the ride angle. The issue is that past a certain speed (maybe 15 mph) they use a technique called field weakening to provide higher speeds. While field weakening provides higher RPMs it comes at the cost of torque. At high speeds it becomes easier to max out the motors duty cycle. When the motor reaches its max duty cycle it has no more power to hold the nose up and can drop the rider. The only warning currently available is the speed based nose lift to let you know you are at the speed they've set as "max".

The recall will add a new feature that will provide an audible alert and vibration when the board reaches 90% of its available duty cycle well before it runs out of power. Hopefully it works as intended and prevents a lot of avoidable accidents.

There are no breaks, the mirror shuts off, because it's gone over its limit. The board warns you, when it reaches that's limit. There is not much to do about this, because physics