The Adox/Efke does not come with a hardener. It's my favorite commercial liquid emulsion, and I've used it a great deal. There is a gallery on my website called "The Good Old World" which is almost exclusively single coated Adox emulsion on 130lb Arches watercolor paper.
I, too, have made the very simple emulsion in "Sliver Gelatin" and so far I like it very much. To increase the contrast I've added 10% print developer, or soaked the paper in developer for 30 seconds before exposing. Both methods work, though of course the second method is messier. I've also double coated with it, which I have never had to to with the Adox.