Apple Watch

I've been using mine for 4 months. Distance is close enough when walking/running outdoors (I also have my phone with me so it's using the phone's GPS) - on a known 1-mile distance it's within a couple hundred feet. I've compared the watch's heart rate monitor against the grip monitor on cardio machines and also manual palpation (counting it at the radial artery) and it's usually within 1-2 beats. Like any other HRM, it's useful for steady-state cardio, not so much for other stuff (e.g. weight lifting). The number of calories burned (overall/daily) matches up pretty closely with the online TDEE calculators I've used. On Monday mornings, it gives a summary of the previous week showing calories burned, distance traveled, active time, etc. and prompts you to set your daily calorie burn ("move") goal for the week - if you exceeded your goal every day the prior week, it will keep bumping it up to motivate you to move more (but you can manually override it if you choose).

The "rings" (move, stand, exercise) motivate me to move more, just like my old Fitbit did. I find them to be a good reminder because they're there every time I look at my watch, showing how much I've done (or haven't done, if it's a lazy day). It makes me want to get at least 30 minutes of exercise in every day, even if it's just a brisk walk, to close that 'exercise' ring. Even if the HRM and distance/steps weren't particularly accurate, I'd still like it just for the motivation it provides.

There are more sport-specific training watches which I'm sure are better suited to 'serious' athletes training for specific goals, but for the average person who just wants to move more, get in better shape and have an idea of how much they're moving and how many calories they're burning, the Apple Watch does a fine job IMO.