Comment by LeifCarrotson

It matches my lived experience.

My body battery and stress often starts declining for no apparent reason and then 12-24 hours later I feel the symptoms of an illness. Similarly, when in a tough training block, HRV is a great tool to gauge how hard I ought to be able to go: I've tried to push through and just do a tough workout anyways when it's out of range, but failed to complete the workout in good form, or felt superficially crappy but had good training readiness according to the watch and was able to do better than expected.

The same holds true in the other direction, I don't log into Connect or scroll through the multitudinous widgets of data often enough to really keep tabs on this stuff, and when I get sick or feel good or bomb a workout or succeed at a workout when I felt off, the metrics consistently back up the actual results.

Personally, I've been thinking about jumping ship to a Coros Apex 4 if my battered Fenix 6 ever gives up the ghost - Garmin's prices are insane these days. At $270, this is cheap enough in comparison to a $1200 Fenix 8 Pro to take the chance. I could buy this and a $480 Apex 4, and then decide I didn't like either of them and go back to a used Forerunner 955, before spending as much as a new top-end Garmin.