I've been using it since 2019, or maybe before.

Overall, it works. I've been thinking about switching to Tutanota, because Proton keeps changing their app interface, and never for the better. Their web interface has a custom editor that's had some annoyance-bugs for years. Also, they limited the number of folders to three.

It hasn't been bad enough to make me actually switch yet, and I haven't had any issues with sending or receiving.