I’m unsure why he mentioned a good amount, as I am across several large spaces on the matrix using Synapse and have accumulated approximately 30GB of data in >1 year. I must clarify that I am the sole user of my instance.

It’s definitely not bad, it has some features discord is still missing. But if you looking for an alternative it’s for sure the thing to check out! Also it is opensource which is quite neat! https://github.com/orgs/revoltchat/repositories