I've been following this add-on for a long time and finally had the chance to test it today. I tested the add-on on its official site at
http://demo.xen-concept.com/ and encountered some issues.
I created a quiz with 2 questions, and even though I selected the correct answers, it still marked them as incorrect. This suggests that the add-on might need further development to resolve this issue.
Additionally, I have a personal suggestion: It could be more engaging if a leaderboard were added to the add-on, where the rankings of successful quiz participants could be displayed in the sidebar. Also, adding a time limit to quizzes and fixing the issues mentioned above could make this add-on much more successful.
It's easy to use. We've chosen to break it down into several steps: creating the quiz, then creating the questions, and once everything's finished, just publish it for members to see.
This means you can create your quiz and publish it whenever you like, and you can simply by adding, modifying or deleting questions.