Have you gone to their website?
I was like you and really almost got caught up in associations, certification, buying all kids of books etc. What I would do is email the AMBA owner and ask them the benefits of their organization. Also email other organization owners. Look at what they have to offer, and what you need. I can start an association tomorrow, and have 100 members. Would that make me better or worse than any other association??? Research everyone you are thinking to join, and if you find one that gives you what you feel you need, good blessings. Don't let anyones opinion or bad experience deter you. What is good for you, just might not work for them