What's the value proposition relative to the alternatives?

It is adding weight, complexity, and limiting choice to your eye-wear while effectively doing a similar thing to half a dozen wireless earbuds already on the market. It isn't really comparable to Google Glass, because Google Glass used projection onto the glasses themselves (creating a unique value).

Plus Amazon are trying to integrate with the US's predominant eye wear monopoly (via insurance/out-of-network frames) instead of just bypassing it and producing the lenses themselves. So you're paying $179.99 for empty frames and then untold amounts for the actual lenses, and trying to ingrate with an insurance system that's designed to benefit only Luxottica (via their stranglehold of both insurance companies AND lens producers).