I moved from Gmail to Fastmail too but I am not that happy. And no, Fastmail does not protect you from the NSA since Australia is one of the Five Eyes:
https://en.wikipedia.org/wiki/Five_Eyes
I moved from Gmail to Fastmail because my personal CRM's mail integration depends on Apple Mail. Gmail and Apple Mail do not go well together because Gmail is not IMAP (and Apple Mail has some issues too, even with the latest improvements). So with Fastmail's 'real' IMAP implementation, that issue was resolved. But Fastmail is lacking in comparison to Gmail in many areas, just two examples:
Filtering: Spam, phishing etc. filtering cannot compare with Gmail. And for your own filters, you cannot create them directly from a mail and see immediately the result as you can in Gmail. You have to create your filters via the setting menu and have to manually check if they actually work …
Security: I use 2-factor authentication as often as possible. Gmail has a very balanced approach to 2-factor authentication. Fastmail on the other hand does not allow you to use 2-factor authentication as a general security measure but only as an _additional_ login. And the configuration is not user-friendly. And since it is only an _additional_ login, you do not get (or need) backup codes or another backup way for your 2-factor authentication like SMS.
Fastmail works fine as a very traditional mail provider but that is not far away from what hosting providers offer anyway.
Your mileage might vary of course. If you are looking for a traditional mail provider with reliable IMAP support, Fastmail is certainly a great choice.