Can I switch between the Play Store app and the direct APK on Android?

Yes, but not by installing one over the other. The two builds are signed with different keys (Play manages its own signing; the direct APK's key is ours alone), and Android refuses to update an app whose signature changed, so the install fails with an "App not installed" style error. Switching means: confirm the app shows "Synced", uninstall the current build, install the other one, sign back in.

Uninstalling clears the app's local data - that is why the sync check comes first. After signing in, everything returns from sync. Have your 12 words or a sign-in QR from another device ready before you uninstall, not after. The builds are otherwise identical; they differ only in how they update and in how Pro is billed.