This post is referring to beeper mini. It’s confusing naming, but that’s not the same as beeper(cloud service). Beeper mini is available to everyone on the play store and is not a cloud service. You just get it, login to Google (to pay the subscription cost) and it works. No invite needed
Sounds like you’re an iPhone user, or at least someone who doesn’t have kids with Android phones and doesn’t participate in group activities where the people primarily use iPhones.
I won’t bother explaining it all, but the real issues are group chats that contain both iPhones and Androids, and image/video quality, reactions, etc. The issues are bad enough that kids especially get left out of group chats over it, and bullying incidents are widely reported (and I’ve seen it first hand)