How can I backup/restore an app (not just it's data) in iOS 10? One of my apps got a big update with some mixed reviews, I'm interested in trying the new version, but won't do it if I can't roll back. For pre-iOS 9 systems, I heard you can backup ipa file from iTunes on PC, update the app on iPhone, and then if needed, overvrite back from iTunes and sync. But it doesn't work now - there's no ipa file for that app after iTunes sync.

What are my options? I've heard about programs like iMazing, but have a feeling that for iOS 10 it will just restore the app data and not the whole app version.
Do an iCloud backup. iCloud backups are snapshots of the phone as it is. So you'll keep the old update and its data with an iCloud backup.

Do 1 right now and the other after the update.

After your testing, then you can over write that latest backup if need be based on your choice.