"very rare prototype enfield ww1 spare mag. Carrier for smle rifle" (?)

[Roger Payne]

I have no axe to grind here, & I do not know for sure whether it is what it claims to be, but the general standard of manufacture of the steel box does not look to be what I would have expected on a WW1 (or possibly pre WW1) piece of equipment.
The tensioning spring at one end is a SMLE mag auxiliary spring (though I suppose that could have been found satisfactory & used).
But what I find most surprising of all is that something so 'hard & pointy' would be accepted into service to be used by Tommies who would risk at best bruising ribs, if not breaking them, when throwing themselves around with something that rigid on their belts.
I have seen the approved 20 round magazine pouches, & these were made of leather - much more suitable.
The EFD stamp does look good, but it could have been copied, or a redundant & already marked piece of brassware could have been used in the manufacture of this piece......just as a SMLE mag spring was.