Preventing transmission was never the point. Reducing deaths (to the tune of 19.8 million lives saved globally, Lancet link in my comment there), was. The "never tested for preventing transmission" argument is thus a red herring. Congratulations on caving in to inflammatory media distortion, I'm sure their ads appreciated your eyeballs.
We don't know that. They never released any statistics from North Korea and even if they do, it'd be quite questionable.