I'd never used a FitBit or similar fitness tracker before getting my Apple Watch, but I had been a huge Garmin GPS watch fan for running and biking in the days before my iPhone had enough battery life to last for a run with GPS enabled.
At first I thought I was mostly going to use the Apple Watch in conjunction with planned activities like running a few miles - I certainly use it for that, in conjunction with Runkeeper - but now I also use the passive activity tracking to keep track of how I'm doing throughout the day.
I won't say that it's strictly because of the watch, but I'm now about as fit as I've ever been, and I think the easy glance over to see where I'm at is really helping with that.
I will gladly credit my Fitbit Aria scale for the same result.
Interestingly, it is less for the feedback if gives me in the short term and rather the long-term graphs. I know that if I want to manipulate the scale up or down in weight and fat percentage, I have to be consistent over really long periods of time. I almost never miss days running or at the gym, my days of heavy drinking are long behind me, and I feel orders of magnitude better than I have in years past. These systems really are fantastic tools, and show that the application of game mechanics can be a force for enacting strong positive change on a personal level.
But at the same time I'm hesitant to wear one of those devices without reasonable guarantees big brother is not collecting data. Therefore, something like AsteroidOS seems ideal: http://asteroidos.org/
Some reading:
http://www.dcrainmaker.com/2014/11/winter-gadget-recommendat...
http://www.dcrainmaker.com/2015/12/garmin-forerunner-630-dep...
Polar, TomTom etc have similar devices, but Garmin are probably the default choice.
But I'd prefer something with a bit more features. Something that can replace very very casual smartphone use. Receive a short call, navigate somewhere. And track my fitness all the time, including HRM w/o band and blood pressure.
Do they have a hardware compatibility list?
From there you can analyze the data. You can't export directly using the app, but you can view all records or find one of many apps that support HealthKit which may possibly export for you.