I would say the main difference between OCMB and ESMB is that ESMB is more for ex-members. On ESMB people discuss old friends, the technology, family still in, how being in affected each person, etc etc etc. Some people there are not necessarily critics, they are just going through the process of leaving the organized church.
This board is more philosophical, and addresses the subject from a lay-person's point of view (not using much scieno-speak).
In its hay-day, this board was the place to come for information about Scientology. If someone was going to make an important announcement, it was made here. In the archives there are plenty of posts that were made by people who were among the first to find their way out of the church...and into this group of critics. The posts were shocking and eye-opening.
As the board grew, there was a mix of exes and never-beens, and that mix was uncomfortable for some. People who had never been in just didn't understand what it meant to leave the church.
So a poster here named itsaline/Emma started ESMB to give exes a place to decompress.
Simultaneously a few unfortunate things happened. First, there was a huge falling out with Anonymous, who had their own board (back then it was called enturbulation, now it's call whyweprotest. People here were given the name "OG" for Old Guard. Some of us didn't get the culture of Anonymous at first (e.g. "Anonymous is not your personal army," and "Pics and docs or it didn't happen.") Some anons thought the OG saw themselves as rockstars, whereas Anons didn't like personal credit or attention. Some anons got mad at some members here, and for several days spammed the board with porn and gore. Added to that was a massive, unrelated wave of spam (that continues to this day). And finally, the owner of this board who has generously kept it running for almost 20 years, wanted to do less day-to-day work maintaining it.
This is why registrations were closed for a long time. Mainly it was the spam, but the attacks also took a toll.
There is much more to this...this is just an outline basically. There have been lots of squabbles and disagreements. There have also been friendships, activism, and even shared joy(!). People have come and gone. I have personally met at least a dozen people who post here, including Andreas who came to California a few years back.
There isn't really any animosity between the boards, because they all serve a different purpose. I read ESMB all the time. I don't post much because I don't feel like I have much to say that is relevant, since I am not an ex.
I have a lot of friends on WWP, too. Many people on this board joined with Anonymous to protest the church, starting in 2008. We protested every month for over 3 years, and still do so, but less frequently, if the mood is right, and there's some reason.
"A man may build himself a throne of bayonets, but he cannot sit on it." -William Ralph Inge
Watch the Los Angeles press conference here: