Same here! Have been using fastmail for ~6 months now. I was hesitant, thought I'd miss push mail on iOS but it has been just fine. Also, there are some iOS mail clients that can push on FastMail (http://mymail.my.com) I always hated Gmail's slow/weird IMAP behavior. Switched to Office365 at some point. Exchange was great but so freaking slow. FastMail has standard, fast IMAP.
I also use the included DNS server for a couple of domains that had been lying around and the static file host for some http placeholder pages and stuff.
Fastmail seems to support IMAP Idle only. And IMAP Idle is not an option for mobile devices since the mail client has to keep the connection open all the time, so there goes your battery …
3rd party apps with push support do not drain battery. They keep a connection open on their servers, and use regular push notifications when something arrives.
I also use the included DNS server for a couple of domains that had been lying around and the static file host for some http placeholder pages and stuff.
I'd never go back to Google at this point.