So, i'll be doing a few days worth of live testing with both devices. They are for sure in different leagues, both feature and price wise.
But for the things that they do have in common, how do they fare up against each other?
I'm not a runner, so i'll be focusing on walks, sleep, overall HR and SpO2 readings.
If you have some request for testing, let me know.
I picked up the Charge 4 since it's one of the few which does SpO2 on a regular basis and has built-in GPS. Other stuff out there either doesn't have those (aw3/4/5) or do it on-demand only (huawei gt2/gt2e).
Fenix 6 Sapphire - Official FW 8.1.0
Charge 4 - FW 20001.82.46
WALK activity
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the results are pretty damn close. Slight advantage to Fenix6 for faster initial GPS lock and somewhat better tracking. To be fair, i think Fitbit's taking some time to do the first ever GPS lock for a new device (they have a support article on that), but subsequent usage should be faster. Will test more over the next days. Also i noticed the Fitbit GPS track is accurate but is displayed somewhat shifted on the map itself. I've noticed this on garmin connect as well if one chooses openmaps or google maps. Not a dealbreaker. Both better than AW (assisted) GPS tracking which cuts & rounds corners in a frenzy.
Fenix 6:
Charge 4:
CONCLUSION:
Time in Hr zones identical
Average HR almost same
Pace faster on Fitbit
Distance more on Fitbit
Total time more on Fitbit
Elevation gain almost the same
Min/Max HR pattern quite similar
More calories reported by Fitbit
Altitude values quite off between the two (Fenix 6 altimeter/barometer were manually calibrated using GPS few hours before)
Fitbit got GPS lock about 20-30 seconds later than the Fenix6 (as i already started the walk), which COULD explain the differences. As i said, i'll test more later on.
SLEEP ANALYSIS
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Fenix 6 (INITIAL values)
Fenix 6 (ADJUSTED values) - yes, they do change if you check back the sleep stats 30min later 
Charge 4
CONCLUSION
Resting HR identical !
Detected sleep overall time better by Fitbit (including initial awake time before actually falling asleep)
Better Fitbit wake up detection (in this case i did toss & turn a lot before actually waking up)
Complete sleep cycles (light-deep-light-rem) can be seen on both devices more or less (esp. 2nd half of the night)
Garmin did not pick up any awake time
SpO2...well, looks kind of similar in the sense that you CAN imagine 4 spikes (towards high) on the Fitbit vs. 4 throughs on the Garmin. They are displaying the values differently though.
OVERALL DAILY HR
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Fenix 6:
Charge 4:
CONCLUSION
I'd say quite mirror-like except one spike which looks more exaggerated on the Fitbit. Dunno, hand movement, band placement or something else.
Will be tested also for few days in parallel.
So, what do you think?
I can't swim right now (duhh) so one comparison i really wanted to do (pool swimming) will have to wait a while :)
Any other comparisons you'd like to see?
