Well, firstly, a small battery charge. Only about 400 hours. However, it is easy to replace it, but in the Polar company store they recommend changing it only for 600, it seems, which is ridiculous, because changing the battery is very simple, although according to reviews, not all of them work correctly. The strap can wear out, and this is almost half the cost, which is somehow not very good. There are two main problems. Doesn't work well with third party apps. It connects every other time and according to an incomprehensible algorithm, while it works perfectly with its own. The native program does not work without connecting to GPS, although third-party programs, if you accidentally managed to connect, work without GPS, but why do I need it, for example, in the gym? Unclear. But the battery naturally eats. Secondly, this very GPS counts very badly - what it depends on is not clear. It's most likely a program bug, since other programs do everything exactly, and it's definitely not the phone (many Polar watches have the same joke). Maybe you can calculate a distance of 2-3 kilometers with real 10, or maybe quite the opposite. This does not affect the calculation of calories burned, but in itself is stupid. The route will remain the same. And I would not say that this is a rare mistake for me. When synchronized with Polar Flow, it will show your routes under your, for example, Google account - to other people. I couldn't find where to turn it off. Does not show arrhythmia, if any.