A few snippets of information gleaned from the Fotoimpex catalogue regarding Efke film:
- do not overexpose and/or overdevelop the ISO 25 and 50 films
- hardening fixer is recommended
-Efke films are made according to old Adox film recipes.
-the layer on which the emulsion is cast comes from Orwo.
-development temperature is critical.
Hope this helps a bit.