I don't know about the others - I suspect they are the same - but Henkels Friodurs and Dovo stainless razors are cryo hardened 440C.
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Is there any way to tell stainless from carbon by just looking? I've ordered a Dovo, but since the bloody page was in German I'm not really sure what I got... :D
My recommendation would be a Dovo Renaissance. It will take as fine an edge as any carbon razor, and will be quite easy to maintain. Really forgiving blade shape too.
See my review in the reviews section.
Stainless is not any harder to sharpen than carbon, some hones are just inneffective at sharpening it.
Appart from letting it get rust, I don't think so.