Using an RSS reader is a popular way to tack OSS apps directly from their source. Obtainum automates this process and simplifies it.
The F-Droid website hosts an outdated version of the APK which causes issues for users who try to install it in multiple user profiles.
F-Droid has issues. Using this method is a way to completely bypass using F-Droid to install open source apps.
If you're going to use F-Droid for apps, there are a few things that you should be aware of.
The F-Droid app repository has some issues that could potentially affect your security.