Yes I know. We've visted Sioux Cener in 2003. There is one particular denomination called the Netherlands Reformed Congregations, the "black Dutch", known for the cold austerity of their beliefs. Wonderful, serious, and sincere people, but with a trace of unbiblical mysticism and leaving a terrible psychological impact on too many. Many in Sioux Center are in counseling for depression because of the psychological damage. Most in these churches believe that they are "unsaved" (though I suspect many, many of them are in fact true and sincere believers and can't accept it.)
You know how many churches have an "alter call" and make it seem like believing on Jesus is the easiest thing in the world? Some call that "easy believism", contradicting the command to "take up thy cross." The NRC is the polar opposite: "hard-believism".