+1 to their import tool. I was really surprised at how good an experience that was. So simple and effective. And idempotent - I had to restart it after re-enabling some of the labels and no dups.
My only issue is the spam filtering isn't nearly as good. I need to regularly check spam.
On that note, I've noticed that the Gmail spam filter has been less effective recently - I get spam coming through to my inbox almost every day now. I've also had some legitimate email going through to the spam box which has very rarely happened with me on Gmail.
If there's one thing that will finally push me to jump to something different it would be if spam filtering becomes ineffective.
Gmail catches more spam than Fastmail does. I almost never get actual spam in my Gmail inbox, though they sometime mark non-spam as spam. Having actual spam turn up in my Fastmail inbox roughly once a week is a little annoying.
My only issue is the spam filtering isn't nearly as good. I need to regularly check spam.