They do have to run servers in order to keep the service alive. If you want to run this stuff yourself on your own server that’s possible using PyPush. The reason they have to run those servers for you is to keep the notification service alive.

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.

Notice how in the article they say "we're not the middle man... Any more"? That's because, up until now, Beeper has been working on a system where they operate as a middle man for your data.

To be fair they never claimed otherwise and all of the code for the bridges are open-sourced and can be run on your own servers so that those servers you control (as opposed to Beeper-owned servers) act as a "middle man" and none of your messages need be trusted to a 3rd party.

To put it simply: only the actual bridge on Beeper Cloud has access to unencrypted messages and you do have the option to run the bridge yourself while continuing to use the Beeper app. You can use as many or as few self-hosted bridges as you'd like.

A few bridges are preconfigured for self-hosting with just a couple of clicks for free through fly.io here