I have compared the three devices a few times, and here is a quick summary of the results :
- Scosche R24 is often giving me a wrong "peak" at the start, during a few minutes, much like my old chest strap. Quite weird from an optical device ! After that, it seems to be really good. Plus long battery life, and it can record without the watch (the distance estimation is crap though), as well as measure HRV for recovery tests. I'm still not so happy with this peak, it can mess the average a bit... It can also record your feet cadence and bicycle cadence too (is this reliable??). The mobile application is a bit limited. It feels like a device where they tried to put a lot of features, but some are not really polished enough (Scosche is NOT a sport company after all !)
- Polar OH1 seems very reliable. It's often the exact copy of the Scosche chart (minus the peak). Very small, battery life not as good as the Scosche, but enough in many cases. Can record alone also. Button is a bit small and not that easy to use. Currently, it's my favorite device. The mobile app is quite nice, but I don't use it much, except for comparison when recording on the device itself.
- The 6X is doing mostly fine during workouts. It's often very close to the Scosche & Polar. There is more differences than between the two arm straps though, but I was pleasantly surprised by the quality of the recording. The average value is often spot on. I have to wear it really tight enough, it can make a significant difference, maybe since I have a hairy skin. There are times when the value is more significantly off, possibly because of how tight I set it on my wrist. And if I'm going for a run in very rainy or cold conditions, I wear it above my jacket, and the OHR can't be used anymore. But whenever I forget to use the arm strap (or if I'm too lazy or in a rush), I find the Fenix 6 to be reliable enough. The F5X I had before was not that good, I tried to avoid using it for my HR.
The combo F6 / Polar is my favorite now. The peak on the records of the Scosche is annoying, and it's a bigger device. Unless I need it for a really long race, I can leave it at home and keep it to measure HRV things. The Polar is cheap and easy to use, battery is quite decent, I don't really feel it on my arm. Easy choice in my opinion if you don't like to wear a chest strap and want more reliable HR stats. Finally, the 6X is doing really fine, I can definitely use it from time to time as a backup solution.
I won't comment on the OHR for the rest of the day, I use it but I don't need it to be crazy reliable (and my other leather strap is a bit lose...).
