A Fastmail account was the best technology purchase I made last year.
I think the main selling point is that there's actual support when you have trouble. And it'll get some of your data out of Google, which has become a bit of a trend among techies.
It seems that the probability of needing a number is also relatively small, since Fastmail has many domains available:
https://www.fastmail.fm/help/signup_domains.html
Of course, the $10 account is not really useful, since it comes with only 250MB space.
I'm not complaining about 40$, but the laziness and friction on changing provider of my identity is still there. And I can't really test how it would work until I switch completely to it with my primary account, since using secondary account is not a real world test.
I like Fastmail, but I need contact syncing, so I cannot fully switch until they've implemented that. And I'd miss the excellent GMail Android app. Especially it's search functionality.