I have to say FastMail works really well on my Apple devices. iOS and macOS have worked perfectly so far for mail, calendar and contacts.
The only pain point was 'losing' my custom domain Google Account when I cancelled G Suite. Migrating mail, etc. wasn't an issue as FastMail has a pretty solid import tool. However one area that caught me out was export/import of my 800+ YouTube subscriptions (that number shocked me aswell).
Turns out YouTube has no such functionality so I ended up having to hack a semi-automated solution but even that wasn't straight forward as YouTube has limits on how many new subscriptions you can make in a ~6 hour window.
I wish Google had some kind of "convert my G Suite account into a consumer Google Account" function instead the moment you cancel the G Suite plan any accounts simply vanish and you then have to sign up again for a consumer Google Account. Quite the pain in the ass.
Anyway it is nice to be free from Google's core services and I am very impressed with how smooth migrating to FastMail has been. If anyone is thinking of doing the same and wants to know anything specific feel free to drop me an email, info in HN profile.