DE blades are cheap and - as they are composed of a single sheet of metal - they're easier to recycle than more complex and expensive cartridge blades or disposable razors.
But since avoiding unecessary wastes was also a factor in my switch to DE shaving, I have ordered a used Siemens DE blades sharpener on eBay, and I've tested it on my dull Merkur Super blade :
I assumed the sharpener would be either ineffective on modern stainless steel blades and the blade would not regain sharpness, or I would loose the coating and the edge would rust, or it would change the soft/aggressive profile of the blade...
It turns out it's an effective device : that dull blade is now as good as new and as soft as it was. No rust so far. When I shaved with it, I had the feeling this blade was brand new.
I still need to test if the blade can still get 5 to 6 shaves though. And I don't know how many times you get to sharpen a blade before the edge is not exposed enough anymore.
Unless some zombie invasion occurs and I can't get new blades anymore, I have no real-life use-case for such a device : to me, it's only a nice-to-have curiosity. Maybe it can be useful in the case of specific hard to find blades ?
In post-WW2 Europe context, this kind of device makes perfect sense : every raw material was scarce and in high demand, especially steel. DE blades would be more expensive than they are now, made of carbon steel prone to rust, and often not available in stores.
