Fastmail user here as well. I use their built in web interface though because it's so good. On mobile I use the app, which I think is just a glorified web app but it also works good.

I still have to maintain my gmail/google email for work but I use fastmail for all my personal stuff.

Very very happy customer. I also do static domain hosting with them.

Exactly the same. Custom domain.

I like their clients (android, web).

I use their notes feature too, for stuff I want to sync.