I like it so far, seems to work reliably and the client is leaps better than any other Matrix client on iOS.
Haven’t checked out the option to self host the bridges yet but it’s on my list.

“For example, if you send a message from Beeper to a friend on WhatsApp, the message is encrypted on your Beeper client, sent to the Beeper web service, which decrypts and re-encrypts the message with WhatsApp's proprietary encryption protocol.”

So, not really end to end for most common use-cases.