I believe it saves a reader-mode version of whatever you feed it, by default? I also pull a copy into my Obsidian vault using the plugin/api, but it's easy to implement with the api if you don't want Obsidian too. Makes it very easy to refer to articles from notes later! (or just rip out everything except the part I cared about.)

I've saved shopping carts and logged-in pages regularly, so the markdown reader version in the apps should definitely be independent of the article/page itself being up.

Can't say I've used pocket, but I think the newsletter-saving (generated email addresses), open source/selfhostability, and api were differentiators that made me actually start using Omnivore - I wouldn't trust closed source and with premium options for something like this.