The E2EE in matrix is actually based on the double ratchet from the Signal protocol. So you could think of the E2E in matrix as just a federated version of Signal. :)
A point in moxie's favor is that the e2ee ux in matrix is currently extremely painful. I'm willing to use it on a couple rooms that consist entirely of geeks, but don't want to subject non-geeks to the whole verification process.
Not only UX, but there seem to be some subtle timing (in non-crypto/non-security meaning) issues.
I ran Synapse on a resource-limited machine, so it had sort of "lagged behind" (or something like that) a little bit now and then. And I saw a number of "error decrypting image" and similar issues. It had self-resolved somehow after a while (saw the message decrypted the next day) but that's still a problem.
Haven't reported this because I have no idea how to collect any useful information.