FRIODUR J.A.HECKNELS ZWILLING double edge razor blades ( discontinued ).Any info ?

Found a shop that has some stock of these :

I was aware of the " Friodur " straights from J.A. Hecknels Zwilling .
But did not know about those DE blades.Of course they are discontinued ,
but the place where I 've found them still keeps a stock of those .
Any further info about them ?
Has anyone tried 'em ?

(They sell for about 4 € per pack of five blades )

That's a fun find. How long has the shop had them in stock?

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I'm open to adventure.  Perhaps you are too.  I suggest you buy some (or all) and try them out!