Ohh, man....well....that's not _entirely_ the whole story. Yes the initial goal is that collectors from all over Europe would bring cabs, BUT (as mentioned on the site) everyone who is interested in this hobby and may not have room for a cab (or just haven't come around to get one yet) is just as much welcome !
The only real obligation is registering through a forum that I frequently visit. We didn't want general public to walk in because we simply cannot handle that organization wise, but also because we're not allowed to at the clubhouse.
Anyway, you're still welcome if you want !