I saw this and had to share:
There was a similar device made of ordinary 20 inch unicycles (without the fixed center pole) at Maker Faire last year.
And one loose unicycle that a diligent young lady was very near to figuring out, apparently for the second year in a row. Spent some time talking with her father about this forum, unicycle sourcing options, etc, wonder if they ever got one.
If there had been one of these in a park near me when I was growing up I still would have ended up arguing with my sister about who sat where!!
Four posts down Barnstar, a few more posts and you will be famous just like me… !!