strap heart rate is quite a bit more accurate, especially for non-steady-state exercise.

As someone who does not train by HR, I appreciate the convenience of the optical sensor. But if you actually rely on HR data, the quality of wrist-based sensors is simply not there. It also seems anecdotally to be worse on the bike than when running.

there's a reason that Garmin won't let you use the built in optical sensor for HRV Stress Test. It's simply not reliable/accurate enough. Not that you need to do an HRV test ever for any reason, but it's telling that they acknowledge the limits of the sensor in that way.

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"Non est ad astra mollis e terris via." - Seneca | rappstar.com | FB - Rappstar Racing | IG - @jordanrapp

I bought the 935 in June and learned a little later how to broadcast my HR to my 510. I can't speak for anyone else or their experiences with this setup. I can only tell you it's been accurate as far as I can tell through my IM build.

This is the reason I bought the 935 (I had the 920).

YMMV

I have had the 935 for several months now. It works great. The wrist-based heart rate seems very accurate. I also have the tri-strap to get HR during the tri-swim, but only use it for races. The broadcasting is easy to do- use the lower left button to scroll down to the HR widget. Once there hold down the middle left button. Then select HR Options (by hitting upper right button). You can then scroll to Broadcast HR and select it. As long as you are broadcasting the only thing you see on the watch is HR. Unless you are doing intervals, or the strap is loose, or you are riding cobbles, it seems pretty accurate. For more info read the DCRainmaker review. It is also easy to upload workouts to TrainingPeaks and other apps. Only down side is the basic design- wish they would hire away some of the Apple watch designers and make the watch look cooler, so it could be worn all the time.

I wear a Scosche Rythym+ on my upper arm. I find that location provides much more reliable results than if worn on the upper forearm which in turn is a much better location for an optical sensor that the wrist.

This!

It might be better on a road or TT bike than while running. The watch can bounce quite a bit while running and that leads to gaps in the distance to reading against the skin. Road cycling is usually not as bouncy and you *should* get a decent read while using wrist-based optical HR. Or at least better than running.

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I considered the Scosche before purchasing the 935, but did't like the idea of having a forearm tanline. I hated the chest strap and find the wrist HR pretty accurate.