I suppose you could say I have one - actually I have three.
I started with a Garmin FR 405, got a FR60, and recently upgraded to an Garmin FR 220.
I am an avid runner, and they all track my workouts. The 405 and 220 are GPS watches. I have heart rate monitors (chest-strap, which I trust a thousand times more than a wrist-based solution at this point). The 405 was fairly large on my wrist, but the FR60 and 220 are actually reasonably sized.
They revolutionized my training when I started wearing them five years ago. I can get instantaneous feedback while I run, and I can track mileage and pace information over an entire season. I run faster now because of the Garmins, and my workouts are more intelligent.
Granted I only wear them while working out. I like not having to strap a phone to my body to get additional data, and I like that they are dedicated devices for the task. The FR60 goes months or years between battery changes, and the 220 can do a long weekend's worth of runs on a single charge. As just a watch the 220 can last weeks between charges.
The rest of them time I am content pulling my phone out of my pocket to check the time, see alerts, and so on. The Pebble is interesting (mainly because I see it as letting me know how important that last vibrate from my phone was), but I simply cannot justify it yet.