I never used Efke, but a lot of folks at Flickr did. And they often tell how they used it.
Fir instance (at random):
To see "all" Efke 25 or Efke 50 images, use this link, brows and ask questions:
You'll find the discussions in the Efke group here:
Back to your original question: what to save/use it for? As I said before, I never used Efke, but when I look at all the images, my first guess would be street photography.
But the better question might be: what kind of photography do you like - or would you like to try once? Since you probably won't be buying\getting Efke film again, I would use it only for a single (ongoing) project, to get an even style in images.
Your own "oneshot Efke project". ;-)
I'm not sure if I was any help, but let us know what you'll decide and will use it for. Would be nice to follow your project.