Since most people using devices without Google Play will be in China, where
Google is generally blocked, instead direct people to f-droid.org unless
they have Google Play installed.
This automatically detects whether Google Play or FDroid is installed, if
so, clicking the promo app button will take the user straight to the
install page. If neither is installed, then the user is taken to the page
for that app on https://f-droid.org
Hans-Christoph Steiner
Nathan Freitas