This would be insane for anyone outside of HN. $10 a month for a 5 person chat? They know everyone can get this free elsewhere for decades now? A 5 person Signal group would even have higher security.
Why is it higher security?
In Matrix you've got to remember to turn on the encryption, and verify each of your clients. At least that's my understanding, maybe that is out of date.
Before you had to verify each pair of (sender, recipient) devices. This meant N*M verifications.
Now you only need to verify a new device when you are setting it up and each new recipient when you start talking to them for the first time. So it's N+M verifications.