The glasses the way they're designed are smart, not in between but rather in a fixed spot and only a part of the field of view. I definitely wouldn't want a computer screen between my eyes and 'the real world' in normal day to day life. Believing what my eyes see is important to me and with another layer in between you'll never know whether you are reacting to an overlay or the real thing. Especially if the images are created with input from a remote source which opens all kinds of interesting possibilities. Superimpose a picture of a traffic accident on the glasses of someone that is driving and you could very well end up with the real thing.
Seeing is believing they say and the response to visual input can be very reflexive. Audio alone can be distracting enough.
So google seems to have that part done right, it'd be great to play around with these.