When you've only got 3 comments on your whole front page, not sure invite-only is the best idea.
This is the main problem of the "Hacker News for [x]" type sites. Lobsters got lots of people interested, but it is itself mostly not interesting to read, because there is very little discussion. Sure, you keep out some noise, but you also keep out what makes hacker news great, and that is the comments from all sorts of people. All these kind of sites serve is a curated link list, which can be nice, but they don't fe…
Their verification method already seems to be enough of a gatekeep.
>if you don't know (or can't find) an existing_user from whom to request an invitation, you can make a public request for one. This will display your name and memo to all other logged-in users who can then send you an invitation if they recognize you.
And they ask for some personal website to verify as well that is visible. Given the volume at this scale, this could have been a manual verification by the creator for a while until there's enough scale to rely on invites (similar to Tildes).