Apk extractor from F-Droid doesn’t seem to work. App in question is Typewise Offline (android keyboard with hex-shaped keys).
EDIT: Probably worth a separate post at some point, but this is one of the few apps for which there is no open source equivalent, TTBOMK, and one of the few remaining proprietary apps that I rely on.
Yes and no. It is more if they are intended to call home once installed. I have backed up some apps and installed them on a second phone without issues. It does depend if they call home via the PlayStore. I can tell because I do not have the Playstore installed on my phone. Some apps will try to reach the Playstore Pay(?) API to confirm if you have bought it. So even if you did before, it will check, anyways. Like, Tasker will constantly check, while some games or icon packs may not. Specially the ones that are an one time purchase.