tbh, I've been using the official app on iOS for years and it's…fine. It's certainly gotten more attractive as of late, but I really do prefer it to Apple Mail. I also directly use the webapps on desktop OSes and they are also fine.

Similar boat. I think the FM iOS client is fine. It’s not a native app, it’s a bit sluggish occasionally, the interface has improved over the past 5 years but it’s still not up to the same scratch as Gmail or Apple Mail. I use FMail2 for macOS. It works fine too. Not polished, no, but it works fine.