Looking at the setup code here, this looks a lot like SSL reinvented over Kafka (instead of over TCP), which is not a bad thing, just the mechanism feels a lot like you've automated a tcpdump into the protocol by making the handshake packets persisted in the stream + committed to disks.

This somewhat makes sense if you're going to buy Kafka from a cloud provider without the ability to trust them, but the trust here is not very useful beyond securing transport trust.

E2e for Kafka usually shows up as a mechanism to encrypt each item differently, because that has a bigger use-case in it.

Kafka being an immutable log, there is no way to go back and delete data for a customer who asks for a data deletion or legally mandated GDPR data removals.

Being able to shred the keys is very useful if you have a destination or source attribute based keys - instead of purging data out of the kafka log you can throw away the key.