Wow, thank you, these are looking interesting! I'm very tempted to try them out!
On the other hand, I would like to know more about the material. They mention Amazonian Indians protecting their feet with pure latex. That 's probably fine for Amazonian jungles, but perhaps not for asphalt and abrasive trails. I mean, I work with liquid latex to make home felted slippers less slippery. Several layers of latex are fine inside the house but would rapidly be torn to pieces outside with just walking, let alone running. For Indians (and myself) it's of course quite easy to give it a new layer, if the previous one is worn out, but I wouldn't expect to have to do this on shoes.