I have an Airnimal Joey, built it up in 2006. That is a 24 inch bike. I built it up with 507 wheels, 520 was the other option.
A folding bike is a compromise. The designer either prioritizes rideability or portability. More portable means less likely to ride really well. The Airnimal Joey rides quite well, almost as well as one of my touring bikes or road bike, but is not very portable. If you want maximum portability, buy a Brompton. I prioritized rideability, I bought a 24 inch folder.
I can put my Joey into an S&S case for non-oversize airline travel, but that is the smallest case I can pack it into. And I have to spend almost as much time to pack the bike in that case as I would spend packing my S&S bike in that case. I have only flown with it once using that case. So, if you want a bike to take on a plane, maybe buying an S&S coupled bike or a Ritchey Break Away is a real consideration instead?
It still is more portable than a full size bike, but if I wanted a bike that I could ride to work on, then fold it up and put under my desk at work, the Airnimal is way too big for that. I think most people that want a folding bike would be better served with a 20 inch folder, or if portability is a big priority, 16 inch.
A couple photos of my Joey at this link:
Folders in the wild - post your photos
Why did I buy the Airnimal? I had a job that had a lot of travel, I was thinking it would be nice to have a bike that I could take on airplanes. And at that time, most airlines gave you two free checked bags so I could take it on a plane for free. That was why I bought the frame and built it up.
But, soon after that, the free luggage ended. And my job changed to one with a lot less travel. The bike no longer had a purpose. So, I have not ridden it much at all. Have not rode it at all this year, not sure if I rode it last year or not.
The trip where I took the photos at the above link was a van supported ACA trip. The Airnimal Joey performed as well as one of my touring bikes or my road bike would have, so it was not a disadvantage to have taken it. But, as I noted above, an S&S coupled bike or a Ritchey Breakaway could have served that role just as well.