On coasting:
Someone who is really good at coasting, like Sem, is probably not having a huge energy savings over someone who is just learning. Since the balance envelope is so narrow, it eliminates anyone not capable of staying in it. For those who have figured it out, it is a constant state of tension, moving the unicycle around beneath you to stay in control.
For coasting to work, at least based on today’s knowledge, you have to have at least two contact points between your body and the unicycle. Traditionally this is your crotch, and a foot (or two) on the fork crown. With only one point of contact with the unicycle, you have nothing to lever the frame with to keep it under you.
Coasting like this doesn’t work:
(yup, we thought about it 20 years ago)
As far as efficiency, coasting doesn’t register. Sure, there’s minimal friction in the drivetrain, but the rider has to exert lots of energy to stay in that tiny balance envelope.