Release development versions through Play Store's Beta Program

[Clubfan22]

Currently, alpha/development/test versions are released on https://redreader.org/alpha/ and F-Droid, both of which require allowing the installation of apps from "untrusted sources", which may be considered a security risk.
To reach a bigger audience (thus more testers), these builds could also be released on Google Play, which allows users to opt-in for beta versions of an app they have already installed: https://support.google.com/googleplay/android-developer/answer/3131213?hl=en#open_beta

I don't know if it's worth the additional work for you but I think this could be beneficial for both users and you as a developer.

[QuantumBadger]

Thanks for the suggestion. I used F-Droid partially because of how easy it is to automatically upload new releases (from a Bash script), and because changes are immediately available rather than having to wait several hours for Google's checks.

It looks like Google have added an API for automatically uploading APKs, although it's not clear how much work this would entail:

https://developers.google.com/android-publisher/