Searching the forums yields mostly comedic breaks, though there is one thread on "Folding Bike?" where it is mentioned kind of seriously.
Main cons I see:
- balance (a lot of sub-cons here, like keeping your weight on seat and not pedals)
- low speed
- not normal, goofy, people looking at you
- relatively expensive, all things considered
I got excited about unicycles just now when thinking about how bulky bicycles are in the van and how they have a noticeable transaction cost of taking in/out. What if I could just grab a unicycle and be on my way? Certainly other perks as well thanks to the small form factor.
I also noticed there are electric unicycles which are actually quite cool but are basically segway for experts and not really fitting the use I was thinking.