Nobody here is talking about all the sensors and cameras this thing has and how easily it can be used for unsolicited audio/video recording? For me this is the biggest reason why Google Glass and other such projects never took off.
Unless someone is actively pointing their phone at you, you can reasonably assume you're not being filmed.
this thing, on the other hand, is supposed to be on all the time. So having your head pointed in someone's general direction is going to be interpreted as "actively filming that person".
This could easily lead to getting punched in the face.