On one hand, I can see the benefits of a beta opening. It allows for a smaller group of people to test out the forum and provide feedback on any bugs or issues that need to be addressed before a larger audience joins. This can help ensure a smoother launch and a better user experience for everyone. In many of my forum openings, I have done the same.
However, I can also see how beta openings can be frustrating for those who are not a part of the initial group. It can feel exclusive and like they're missing out on something. Plus, if the beta testing period goes on for too long, it can lead to a lack of interest from potential users who may move on to other forums in the meantime.