Not so much a "demo", but he does have it running on his site.
nobita.me
You will have to join... and probably to be "nice" clean up any group you create. I doubt you will have ACP access to the back end.
This is a decent groups add-on, but at least for my use, it has several glaring warts that have been brought up in the support site and still not addressed after several months.
I personally hope that XF develops a fully integrated Groups add-on that makes FULL use of calendars for both registered users and guests. I would REALLY enjoy the ability for guests to see calendar events for the general public in the group calendar instead of it being locked down to members in a "closed" group.