What's the difference between Is New User and New User After Start Date?
New User After Start Date would include users on their first session. Another way to answer that question would be literally the first time we ever see them that user.
Is New User is users on their first session. So if they force close and reopen the app, and they're on their next session, that user will no longer qualify for the segmentation of Is New User anymore.
On the push side:
It's a new user that we've seen in the last 7 days.