If you watch it, you will see a glimpse of Wanderer’s real body form. It shows fairly early in the featurette, but it’s there and you can’t miss it. However, if you don’t want to spoil yourself, then don’t watch it, of course.
You’ll also be able to see a little more of the cave, and basically Saoirse Ronan being all buddy buddy with actors Max Irons, who plays Jared, and Jake Abel, who plays Ian.
So far, I don’t really see anything to complain about.