I'm glad that you posted here in the Community, @Am00ngus.
Yes, you're right it is an open-book test. However, some people view this as a crowd-sourced answer which is not.
For example, you might have the access to your textbooks and notes, yet, you still couldn't lean over and compare your answer to your colleague. And to maintain integrity, Intuit doesn't promote third parties who offer preparation training.
Feel free to read this article for more details: Inspiration in QuickBooks Online Certification.
Once you're done taking the test. You can then start your training by clicking on this link: Self-paced training and Accountant University.
If you need additional information about Pro Advisor online certification, never hesitate to reply to this post. Keep safe and have a good one!