Round Case 1

The rings looked a little different, as shown on the product photo.
Mechanically, the rings properly processed, the sliding surfaces are made of metal, the body made of plastic.
The bayonet segments are made of plastic, but there is the Gleitfäche about metal, I see no weak point.
The rings sit with me without clearance, without jamming, which probably comes that all bayonet segments hold the lens, are provided with a spring. How hard must be the lens, I can not say because my lenses do not exceed one kilogram.

The contacts are gold-plated, with all three rings I had no problems.
Both covers are secure clean.

For optical behavior I do not need anything, because the extension tubes have no influence on how the lens used in each case is with the intermediate rings. Similarly to autofocus and exposure, here you just have to try, what else goes with the particular combination of camera and adapter rings. Because simply apply the rules of optics.

Am completely satisfied.