I suppose further documentation is needed to verify that the Krag 'open' sling-swivels were actually produced in significant numbers and were part of the sling tests or trials.
The Mills & Orndorff rifle slings and the haversack & canteen straps did not work out well in U.S. testing.
It is interesting, however, that the rifle sling with some revision, (shorter, no keepers, and wider 'end-hooks'), was amazingly successful for the British on Lee-Enfields, with conventional sling-swivels. The British version served in two world wars under harsh conditions. It is a serviceable 'carry strap' and can be utilized as a shooting sling. I suppose there are many subtle differences in stitching, weave, and general construction, between the Krag and L-E versions.
FWIW - The idea was good. It was a matter of execution.
