Re: 2nd Display
"I always wondered why there was this great desire to run apps on a watch. Surely the processing overhead will eat the device's battery?
"I always thought wearables/smart watches would be best as second displays for a smartphone for things like notifications, current fitness stats, etc. Plus, also, heart rate sensor for fitness tracking."
Pretty much this. When I first bought my fruity wrist computer, I did have a Solitaire app on it. Bad move. The screen is too small, and it guzzled the battery even more than the damned thing does anyway. (The Series 2 is a *lot* better about this, except that now I have a dual-core CPU in my *watch*.)
And you missed one app that it has that I find useful: remote control for the iOS music app, so the phone can stay in the pocket where it belongs. My overall list: time, date, fitness rings, next/current appointment from the phone's calendar, watch battery state, notifications, heart rate check occasionally, and the current temperature from the phone's Weather app.