@Philip The soles are of course quite hard and a not very thick, but for just walking around indoors they are fine. The outer sole is softer than the vegtan inner sole, for a bit more grip. Some kind of thick nubuck. You don't want to slip in your slippers. :)
The heavily oiled/greased/waxed leather in the uppers feels really nice on the feet. Happy with that. For anything you make for outdoors wear a rubber sole should probably be added. Nothing I'd wear in public, though. :) I am a bit worried about stretching, but if they suddenly don't fit I guess I'll just sew in a crease on top of them. I am thinking in the same way you do on leather gloves, the snake-y thing. Could look cool.
As these are the prototypes, edgework is sloppy. Sorry.