I am not too pleased with some of his later explanations - I think he may have been stretching a bit.
For example, being able to ride a contraption in side two minutes could be for any number of reasons I'd guess.
I don't think that riding his contraption within two minutes demonstrates doing anything remarkably difficult. And therefore is no indication of any inherent stability. I venture that I could design an unstable product that people with an appropriate skill set could also manage very quickly.
I have. over recent years, put around 30 or 40 unicyclists of ALL abilities (or disabilities ) onto a giraffe, those tall chain-drive unicycles that performers like to show off on. My record so far is that almost every rider has cycled away from support and a balancing shoulder on the first or second attempt.
A few have taken a third attempt. No one has failed to ride away in control within three attempts.
I repeat NO-ONE has failed to ride away in control within three attempts.
Nevertheless, the physics and geometry is very interesting and I will certainly be using this TED talk to challenge others claiming that it is all about rotational inertia.
I'd love to see someone now tackle the belief that the crack of a whip is a sonic boom. (Yes, I am aware of the much quoted mathematical treatise that was done a few years back but I can also demonstrate where why the learned authorr is wrong.)