(I say this as a longtime user, and this is not meant to be damning with faint praise). Their email is best of class outside of gmail. It even beats in certain ways: It syncs faster. It's not made by a surveillance company. As a paying user, I've gotten very competent tech support. They have very good privacy controls re: image loading. They seem to permanently grandfather rates, which is nice.
Downsides: their label system is, to someone who really likes gmail, not as good. Calendar syncing on Android with their preferred sync app breaks every couple of months until you hit resync. Fastmail is in Australia, and I'm not sure the impact of Australia's police assistance laws.
Same: They support u2f.
Their product has improved a lot in the 5 years I've been using it, and is very worth the money. I think it's critically important that there exist high quality alternatives to google services, so that's a nice secondary reason to pay them.