I was really obsessed with rings on knives for a while: LaGriffes, Kerambits, HAKs, even bird & trout knives. Once one of those things is secure in your hand, it takes a hell of a lot to knock them loose: a quality that I loved.
But try as I might, I've never been able to deploy a ring knife (of any kind) as easily as a more "standard" handle during stress (whether timer, pressure, IFWA, etc). When deploying a ring knife, my initial grip acquisition is always just a hair slower and requires more fine motor control / awareness.
Without looking, I can easily grasp a standard handle while sheathed. When a ring is added to the design, the beginning of my drawstroke starts with the handle grab, but requires an extra step of physically "finding" the ring with my finger(s).
The obvious answer, of course, is more practice. But when I was still obsessed with them, believe me: I did. I definitely refined my drawstroke over time, but there was still always a chance that I would fumble the initial finger placement into the ring.
The fact that this sheath covers the entire handle and only leaves the ring accessible makes this a very unappealing package for me. I'm not saying it's bad; I'm not saying it's "wrong"; it just doesn't appeal to me.