The first thing that struck me is that it’s extremely similar to Siri, except it is visual as well as audible. This does serve some benefits (for example directions) as seeing is sometimes easier than having to listen, especially with lots of background noise.
My primary concern that it just isn’t practical for cost reasons still seem justified. Under the present model by wireless providers you’d need to add tethering to your phone’s plan in order to use such a device as there’s no Bluetooth profile that would facilitate most of that, with the exception of making a call like a normal Bluetooth headset. That’s an easy $20-30 a month via AT&T and $20 for Verizon. Given data plans are becoming more stringent, paying more for less data in a few years is entirely possible.
I’d bet Apple is working on something similar (how could they not be?), but will either use a proprietary Bluetooth profile or an entirely different radio for the purpose. I can’t imagine Apple shipping something that looks like Google’s device does either. It looks too much like eyeglasses and goes across the entire face to provide a tiny screen to one eye. I’d see a Bluetooth headset (Apple had one in the past) with an extremely thin boom and screen. Perhaps gyroscopically balanced (this sounds like a long shot for many reasons). The whole over the face thing seems reminiscent of when cell phones were 60% keyboard.