Upload & Sell: On
Adapters are simply put, a fudge. 'High quality' adapters are a high quality fudge.
Made by different manufacturers, some reputable some not, all of which use different machining processes on different jigs and product that uses different metallurgy, variable QA and product finishing - all made to a price right? Of course you also introduce more slop into the system, by adding an extra 'joint'. These are not childrens' meccano toys, demands on precision grow with every generation of sensor. Very different game from a wobbly sheet of film.
Users put these on a certain body, use a lens from a second maker, using an adapter from a third company, and expect things to work out fine because it all fits, right? They won't do so very often, even using common sense. Roger's findings appear statistically and methodologically verifiable (and the material is free of commercial interest or promotion, please note).
As Roger states, this is for geeks who want top quality, not average jpeg shooters. These results tally with why I only use replacement mounts or native lenses. Research like this might compel them to lift their game, but somehow I doubt it, and this is where the cynicism of commercial interests should lie, not with the messenger.