They’re basically 4 pairs of shoes in one and they are all pretty damn funky if you ask me. They are made by a German company called Nat2. Nat2 also make other kinds of convertible shoes, including trainers that turn into outright sandals.
I prefer these though, cause the trainers look very cartoon-like, but in a good way. It’s basically like wearing Optimus Prime on your feet, if he were made of canvas and rubber.
You can get these from Coilexstore.com. It helps if you speak German.
I’ve also seen a bunch of these for sale for only 20UKP on Mozimo, but in a limited colour range.