I read so many great things about the Polar H10 that I bought one to replace my aging HRM-Run and HRM-2SS. New must be better, right?
After a few months I had a close look at the data in Runalyze (R-R intervals, % anomalies) and there was indeed a small difference in favor of the H10. But when looking at the types of runs, it turned out all trail runs and hard interval sessions had more anomalies on average and easy runs on flat terrain less, regardless of the sensor.
I think it is likely that trail runs/intervals are more challenging for good HR measurement. I had bought the H10 after the summer, and have not done many trail runs with it.
In any case, the Polar H10 does very well and has nice accompanying apps to log data and that can show ECG.