I think they seem like an interesting concept. After a bunch of work from different companies (mostly samsung to my knowledge) they are actually starting to seem viable well exept for the price. But i bet you that we will be getting foldable tablets that you can turn into large screens at some point.

You can create folders and labels, but you need to go to the web version in order to make rules, but it all syncs up with the mobile app aswell. The website also works fine on mobile.

I use protonmail and have a paid account there. They have filters that can automatically move mails to folders or give them a label.

I think there are a bunch of links in the sidebar of this community. Those might be interesting to use if you are new to the fediverse.