Originally Posted by Halk
Plastic does not protect against torsion, it may well protect better against impact, but pressure against one corner or a twisting pressure will break screens, while a metal shelled reader will stay intact.
Now that prices are through the floor though it's perhaps not such a big deal though.
The best way to protect against that is to use a good-quality rigid case, to my mind. I always buy a good case for my readers, and in all the years I've been using them haven't had a problem.