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I had a Garmin 645M for two months and ended up returning it (because of a firmware bug that would cause it to reset sometimes during runs with music playback, losing data). The firmware bug aside (which I assume Garmin will eventually fix, as it's a known issue), it was a FAR better running watch than my AW S3. But, it was also more running watch than I need at this point in my athletic life, and it wasn't even in the same league when it came to smartwatch features.

As for being a general fitness tracker (steps, stairs, HR, sleep, etc), I don't use those functions and don't care to, so I can't speak to that.
 
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