App Links is an "open" solution from Facebook that's poorly adopted by developers. Opener is a solution intended directly for end users that doesn't rely on developer to adopt some standard. Developers usually won't adopt something like App Links, but end users still want to open links in apps. I wrote Opener to fill the gap :)
You're correct, iOS apps can only handle schemes but now whole URLs. On Android, the system can intercept any URL and pass it to the app (http://instagram.com/blahblahblah goes to the Instagram app, for example), which means web URLs can open in apps instead. On iOS, you must use a dedicated scheme, which means links from the web don't play nice with apps.
Opener attempts to fix this by mapping web links to app-specific links.
Totally agreed, Android does a way better job of this. Opener is a stopgap on iOS, but it would be way better if Apple had a first party fix. Rumor has it there's one coming soon.
