Why not simply screwing the hex plug in your DIN valve, so that a standard yoke hose can be used for filling?
This is what I do on my 15 liters Faber steel tank...
As my valve is double post, I usually leave the hex insert permanently screwed in one of the two.
So when they fill the tank they simply use the valve which fits their comprosser, without any adaptor.
However, if you have just one post, screwing in the hex insert takes less than one minute.
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I don't believe this will work for my tanks (admittedly I haven't tried it though).