I attached some more photos showing close-ups of the cradle holding mechanism.

and

The leather (or faux leather?) is much thinner than the K3 cases, especially at the area which folds (hinges). I have no clue as to what material, if any, makes up the layer between the leather and the cloth inner surface. My eyes say this is really thin, but my touch says it feels strong. My instinct is that it would be incredibly difficult to tear it. Leather, and other layers, can be super tough, so I hope this cover is tough enough to last through tens of thousands of opening and closing actions.

EDIT: I just examined the Marware cover I purchased for $35 (only $4 less than the Amazon cover). The Marware is made of faux leather. My guess is some sort of vinyl. Although the cover is thicker than the Amazon case, it is due mostly to padding. The vinyl feels very cheap and thin and I'm thinking it is much less durable than the material (probably leather) used on the Amazon cover. I would suspect the Marware cover to wear out long before the Amazon cover.

The back of the cover is a rubber and plastic cradle covered on the exterior surface with leather and molded to perfectly fit the K4. The K4 in the cover, so K4 plus back cover, is perhaps 2mm thicker than just the K4 by itself. I have a clip on light that I used with it last night and it worked very well. My clip on light clip is not hinged but has two standard sized clips and the larger one fit like a glove and securely held the light on the back cover. BTW, hopefully the clip on light will soon be a mute point for me as I hope to have the KFire in less than two weeks and will use it for low light reading and use my K4 for reading in well lighted areas!