I dunno. I keep remembering what my old Pebble did, and how well it did, and nothing more... And yep, I want it back.
Basically, a dumb watch, with an HR monitor, accelerometer, and could sync that data to my phone app.
Its API let me do cool things like pause/unpause my music while running, which was nice. But, it required the apps to be have an API for doing so.
Battery? The thing went an entire week between charges.