Same thing that’s been in the news about some sharing info with police. The comment of the messages are ete encrypted but notifications of who is talking to who is not

Beeper Mini’s GCM server only handles a “new message waiting” trigger, it doesn’t contain any private data like who the message is from or its contents, just that a new message is available.

My objection wouldn’t be that they didn’t put in enough effort, because it was clearly a lot, but that the service is a doomed idea.