Multi-user support now available on mobile apps
 

Fastmail Blog post (Product)
https://fastmail.blog/2019/10/02/fas...i-user-support

Does adding a new user still bill the full subscription rate of the main account?
(I'm still on legacy 'Enhanced', so can't add user and check)

Unless someone knows different, this enhancement does nothing for you if you only have a single FastMail user account. I do not believe there are any billing implications. If you have multiple accounts, this helps you switch between them. It does not allow you to add new accounts on the fly.