It was not strong rule of law at all. Germany was chaotic messy place back then. And in addition, courts were right wing biased long before nazi.
Also, the existence of parallel non judicial system makes it literal opposite of strong rule of law. It is not a rule of law when a SA thug can beat and imprison you for winning over him in cards - which was the literal situation in Third Reich.
> Most people would not come into contact with the second system, and barely knew it existed.
Everyone knew about the parallel system. The fear and terror were base of power. There were no attempts to hide it and many attempts to publicize it by nazi.
Moreover, the whole thing started by repression and arrests of high profile political opposition. People do notice that famous writers are in hiding, that the leaders of the strongest party run away, are in prison and then dead. It was impossible to not know about the parallel system or widely publicized repressions. But, a German in question might have been someone who agree with those or benefits from those.