In my experience yes, but some planes ive notice they turn back on each time there is an announcement, so depending on how many it can be annoying. Eother way advertising is a cancer that plagues our lives more and more.

You can, but I've stopped ever using them because the screen completely stops for every. Single. Announcement.

And now you can have your phone out for take off and landings, so yea no thanks I'll stick with my device that keeps working when they're making some random announcement about drinks or some shit

If you still can, they'll find ways to disable the option to turn them off, because it's time you don't watch an ad.