There is no such thing as a free lunch.
The password will give holders access to all posts, but they will enter it manually every time. Also, there will be no way to automatically recover the password if holders lose it.
Registered users may access all articles without having to re-enter the password every time and access a form to suggest topics that they would like to be addressed. Additionally, they will receive a complimentary copy of Upstream and the relevant supplements in eBook format.
If you want to know about the reasons behind the decision of making the blog paid, read this post.