The forum can be quite dead at times, if you check it once a week, there will always be something interesting to read/discussion posts to participate in. Just that itself, I would not say is worth the $150 a year (he does not do monthly). I have not attended any of the events or meetups, found a mentor, or participated in the book club, so I can't comment on that stuff.
The thing that makes it most valuable to me, and I'm probably in the minority, is the "curated list of knowledge" (various books, thought papers, academic pieces) and the additional exclusive emails. I constantly find interesting and thought provoking articles, speeches, interviews, etc. I think that part itself is worth the $150 a year.