Segunda prueba con Amazfit Stratos / Pace 2

Como me da pereza volver a escribirlo en Español, copio pego en Inglés el resultado de comparar el Suunto Ambit 3 Peack con el Stratos. Es mi segunda salida con ambos y ya puedo sacar alguna conclusión.

Second Test:
Suunto Ambit 3 Peak vs Stratos/Pace 2.
17km in a forest in TrailRunning mode
Sunny, 5.Centigrades

Raw Data Suunto / Stratos

Distance: 17,02 / 17,01 (almost identical)
Track: Pretty similar and accurate both of them (see screenshoot). Suunto Blue, Stratos Red

Highest point: 737 / 736 --> similar
Lowest point: 668 / 665 --> similar
Ascent: 291 /338
Descent: 294 / 340
Althoug there are more than 40 meters difference (too much), ascent and descent are similar. This was expected as the circuit was circular.

Battery: Suunto battery is legendary. Between 20 and 200 hours with GPS on depending on the GPS interval. Stratos: I charged it yesterday and it was at 52% when I finished the test. Pretty bad. By this very same token it would not last enough to finish a Marathon (more tests are needed)

Heart Rate: Suunto with HR chest strap, Stratos Optical HR
In this case the heart rate I obtained with the Stratos was rubish.

This circuit has lots of slopes. This means your heart rate is constantly changing. Example, when you are running uphill you go slower but your heart rate increases. And when you go downhill, you go faster but your HR can decrease. This is normal and easy to understand... but not for the Stratos.

Suunto: Graph HR vs altitude --> It is easy to see the correlation between Ascent/descent and HR. For example, look the last km. My HR increased with the ascent.

Stratos: Graph HR vs altitude --> Most of the time the readings were wrong. For example, during the last ascent my HR decreased (ein?)

I suspect is something related with the algorithms and Data Analysis  that the Stratos do from the optical readings and it asumes that, the lower the pace, the lower de HR.

What´s your opinion? Have you observe something similar with your units?