I wonder whether the extra weight of a third, retractable/foldable leg would negate the power savings that could accrue from being able to switch to 3-wheeled mode when appropriate (thereby allowing the gyro to be spun down).
This generalizes fixed 2-wheel dynamic balancers which mostly don’t have flywheels for stability either, the focus is on the dynamics of keeping the wheels under the center of gravity, or a bit offset when moving.
The novelty here is about switching between dynamic control policies while keeping them simple.