- Both desktop and mobile apps are miles ahead in terms of smoothness compared to GMail (though I stopped using it a long time ago, so that comparison could be outdated).
- I'm proxying my GMail inbox and parking my own subdomain email for wildcard addresses. No problems here.
- I have a bunch of saved searches that I revisit regularly.
- Calendar work well with auto adding events from incoming mail.
- Not using contacts book too much, I just know that it's there but I'm mostly autocompleting recipients if needed.
- Recently they added scheduled email sending, that was the last feature I was missing.
I don't think I had to fall back to GMail even once. Fastmail just says what it does and does it well.