Good question.

Simplex chat also use signal protocol to achieve end to end encryption.

https://github.com/simplex-chat/simplex-chat/blob/stable/PRIVACY.md 

"Simplex chat is the first messenger without user IDs. " This is its most distinctive feature.

“To deliver messages, instead of user IDs used by all other platforms, SimpleX uses temporary anonymous pairwise identifiers of message queues, separate for each of your connections — there are no long term identifiers.”

In my view, Keychat's method of changing the sending and receiving addresses for almost every message is more beneficial for metadata privacy.

I think the number of Simple Chat relays is fewer than the number of Nostr relays. Moreover, the Simplex Chat team has not aimed to integrate with Bitcoin in any way. Could it be said that Simplex Chat does not yet have a viable economic model? https://image.nostr.build/79238f0f305dc434ebb1024f60baf422f34c467398b269541642dcad52c50c2f.png