Garmin released a new feature called TrueUp that will sync the data between various devices.
I just checked my Vivosmart HR and, sure enough, it includes all my steps from my 12 mile run this morning that was recorded on my Forerunner 235.
Check DC Rainmaker for all the details.
(He generally recommends that you stick with an ecosystem. So if you have Garmin watch, get a Garmin activity tracker. This feature is a great example of that advice paying off.)