On the Fireside Fedi interview with Jerry ( the admin of Infosec.Exchange Mastodon instance ) a scary truth was suddenly revealed ( on 34:11 ): Just to keep the instance up and running he needs to spend up to $5000 a month, pretty much out of his pocket. Donations to the instance barely cover any of that. And if he will ask people to pay to use it, they will, rightfully so, switch to a different instance.
Feeds can be personal, so you can decide how granular to you want them. So far I’m able to follow every conversation on the different topics I like, so I would say it works quite well so far.
They can be public too, but personally I prefer to customize my own.