I am happy to share that I just passed the PSM 1 exam at my first attempt with 95/100.
Here are some of my experiences:
1. scrum guide itself + open assessments + mplaze exam simulator should be more than enough to pass the exam, please try to understand everything in the scrum guide instead of simply memorizing it.
2. I personally didn't encounter anything outside of the scope of scrum guide, eg. scaled scrum etc, but this may not be the general rule for everyone, it is up to you to learn additional materials regarding scaled scrum or other topics.
3. overall learning time is around two weeks, I read through the scrum guide for at least 6 times and made detailed notes.
4. The overall experience regarding the exam website is quick, straightforward, and responsive, I didn't encounter any internet or connection issues, recommend using Chrome.