I never used a fitbit or similar because I think they are privacy nightmares. I'm also not a big fan of measuring everything (or over-optimizing everything).
But now I'm curious: are there any that d...
It depends on the use case. I mean, most of the watches can measure heart rates, but the results with a Brustgurt are much better and more reliable. Tracker devices are more open (ANT, Bluetooth) and have better privacy options.