I took over a group that was started in 2013. We meet for volleyball and keep an average of 500 members in the Raleigh, NC area. What we get from meetup.com is an app for a couple hundred dollars a year that does just about what Facebook does for free. Honestly, I have been too lazy to move the group... until now.
They are raising their rates, which is not the big deal as much as I tried contacting customer service to learn more about the increase. Meetup customer service is TERRIBLE, and pretty much nonexistent.
So, if you have a couple hundred dollars to burn for nothing more than a posting site, it is stable. We will most likely be moving to Facebook.