What a reader sees in the Subscribe form(s) is a bit different if they are logged in versus if they're logged out of Grow.
Logged In To a Grow Account
When a reader is logged into Grow they will only see a Subscribe button, they won't have to enter their email address:
Logged Out of a Grow Account
When a reader is logged out of their Grow account, they will be prompted to add their email with the text box: