What happens when i select for android "ETC1 (split alpha channel)", but disable sprite packer for builds

Documentation says that "ETC1 (split alpha channel)" works with sprite packer. But which compression will actually active when "ETC1 (split alpha channel)" enabled but sprite packer disabled?

And second question: If "ETC1 (split alpha channel)" is enabled and sprite packer enabled - is this options works when in android build settings i choose "Don't override" for textures.

And third question =) If "ETC1 (split alpha channel)" is enabled and sprite packer enabled - is it means that all android devices will support this compression format? I'm asking because it says here ETC1 and the documentation says that all Android devices support ETC1, but in the sprite packer while browsing the Atlas at the top of the window is written ETC2 .