4 December 2018
We mainly use meetup as a way of publicising meetings, at which it is very good. We also use the RSVP mechanism to get some idea of how many people will turn up to a meeting, but this is very inaccurate - at best, we normally get between half and two-thirds of the "yes" numbers attending.
We do not require people to pay for meetings, or acquire tickets, and we do not "take a register" of who actually turns up. We don't even insist that people have to use meetup to indicate they're coming. It is important to me that this be a free and open meeting.
This does mean that we have a problem when a meeting is very popular and reaches the practical room size - i.e., how many will safely fit in our meeting room (although we've really only had that problem once so far).