The front screen is not even useful. You don't even see the eyes, you just see a uniform blue blob - have a look on anything on YouTube not uploaded by Apple themselves, and you'll see.
The value of the front screen to Apple is that by the time this stuff actually fits into a pair of glasses, they'll have had years of practical experimentation in how to indicate 'person is using the face computer' in settings outside of a dedicated VR room.
Assuming it still makes sense to have some kind of outward facing screen on a pair of glasses.
By "glasses" I mean the form factor, not something that actually has transparent lenses. Apple is making a (in my opinion reasonable) bet here that trying to actually make a see-through device is a losing proposition.