I don't think (electric included) unicycles will ever have the same stopping performance of conventional vehicles - the center of gravity is just much further forward than in any two-wheeled vehicle. The requirements imposed by the balancing mechanism limits the possible braking force to how far behind the wheel a person can get.
They can still stop plenty fast enough for most purposes, though, and it's a very natural action compared to almost any other vehicle.
On wheel size - yeah, its the case that the smaller the wheel, the more responsive a unicycle becomes to torques applied by a person's body. It becomes a tradeoff between the resilience of a large wheel to bumps and terrain, and the responsiveness afforded by a tiny wheel (which takes less torque to apply a given forward/backwards force)
They can still stop plenty fast enough for most purposes, though, and it's a very natural action compared to almost any other vehicle.
On wheel size - yeah, its the case that the smaller the wheel, the more responsive a unicycle becomes to torques applied by a person's body. It becomes a tradeoff between the resilience of a large wheel to bumps and terrain, and the responsiveness afforded by a tiny wheel (which takes less torque to apply a given forward/backwards force)