By that logic, there's nothing guaranteeing iMessage on iPhones is secure or private either because it's closed source. If you don't want to trust Beeper mini, you'll be free to run their iMessage bridge on your own Matrix stack when they open source it at some point, which they're promising to do (and you still won't know that Apple isn't scraping your messages on the iOS side). When I decide to trust a company, it's because I look at what they're transparently communicating to their end users. Every indication is that they are trying to get out of the middle of handling encrypted messages. Their first move to make this happen was allowing people to self host their own Beeper bridges (which you can still do with Beeper Cloud if you prefer and you will know that your messages are always encrypted within the Beeper infrastructure). They aren't going to release the source for their client ever because that's the only way they make any money.