Is the generated text original/unique?

Not always. Neither we nor our competitors can ensure this a priori. Giving high frequent and repetition penalty to the model, only assures that it will pick the least probable word.
You can check the originality/uniqueness of a text after you've generated the text by searching part of the generated text in Google or using third-party providers, like Copyscape.
We are discussing if integrating a third-party provider in our app in the next release cycles.