Film: Fuji Superia 400
My Fed-5C works! I was so worried about it not working - but it does, and bizarrely it works so brilliantly in natural light. I'm most definitely going to dig out a different film to load into it, because I am so happy with how these have come out - even with the light leaks and other wonkiness that comes from shooting with a camera that has no proper viewfinder.
Basically, I'm am recommending any Fed Rangefinder for anyone interested in 35mm photography. 10/10 - would use again.