I don’t quite understand how this will be different from what built in iPhone password manager.

Something I’d really like: let my iPhone act as a Bluetooth (obviously encryption will be necessary!) or USB keyboard, and have it hold my passwords/type them. That way I could keep my passwords all in one place, and manage them locally. Currently I use keepass when not on iOS, which is fine, but I don’t really want to have to expose my whole passwords file to a Windows machine, since they are traditionally infested with malware (and apparently MS is flirting with including their own first party malware).