I would caution against the bring your own example. I’ve found myself nodding off and getting distracted because while it may seem interesting and important to you, and you may have done something legitimately cool, it may not be interesting to me, you may be bad at presenting it, you don’t have sufficient time to go into sufficient detail, or I may not have the requisite background to understand in the limited amount of time we’d have together. I think it tests things that aren’t a good signal.
Depends on how you use it. If you use the project as a motivation to start a technical conversation it's ok. You had access to the documentation before, so at least you have an idea of the project. If the documentation isn't enough for you to prepare for the interview, that already tells you something about the candidate.
