I don't think that's a question to be asked of Hacker News readers in general, as presumably most of us aren't Substack writers, just readers.
To be honest, I don't like Substack as an application. Their commenting defaults are terrible. I'm not a fan of the push model of newsletters in general and prefer the pull model of going to the site whenever you feel like being updated on your own schedule. But I like the writers, so I go there anyway.