Re: Still need that "killer app" ?
The unique feature a watch provides is the time and date. Instantly. Fusslessly.
Checking a phone for the time or date is a hassle. Try in in the middle of a game. Even during a time out. Your phone's off-court in a bag. Try it climbing a gonzo hill. Try it driving when the car's clock is light-washed. And, if you're doing anything more exuberant than sitting at a desk, your phone might be securely tucked in somewhere not easy to slip out.
Battery? A $15 Casio's battery lasts longer than the pins that keep the band on. And longer than the band, itself. And such a watch can be on you 24x7. No fuss. No muss.
Killer app other than the time? Fashion. Apple, Rolex, and other jewelry outfits have that covered. Boring.