Today, I successfully finished the Scrum.org online test as Professional Scrum Product Owner I. The test comprises 80 multiple choice questions in 60 minutes. To pass it, you have to answer 85% of them correctly. But as many of the questions can only be answered correctly if you really consider the exact meaning of the wordings, I have commit that the test is much harder than the open assessments. Moreover, not all questions were part of the PSPO course we have had before or the Scrum Guide itself and, thus, you had to answer more based on your gut feeling as based on the material you studied.
Unfortunately, the UI of the test is not the same as of the open assessments. After the third of ten questions I had bookmarked to reconsider them again, I accidently hit the submit button, which is placed where the proceed to next question button has been before you have answered all questions once. This could not happen in the open assessments where you were asked twice if you really want to commit your answers now. Luckily, I nonetheless passed the test.