This is the first time I'm using a smart band/smart watch. I initially bought it to measure calories during soccer, basketball, and airsoft, as ideally I would like to see how many kilometers I ran in each activity. I also preferred it because it's visually more attractive than Xiaomi's basic bands.
Here comes the first major downside of the smart band: the built-in GPS only measures kilometers in running, cycling, and walking modes, not in other sports. For example, in soccer it only measures steps and calories, not distance unfortunately. If you try to replace the soccer function with the running function, then the calorie measurement has a big difference (I tried it twice).
The calorie measurement is generally satisfactory in the one month I've had it. On the other hand, the accuracy of the steps could be better as sometimes abrupt hand movements can be perceived as steps. However, this is something that will not happen in 90-95% of cases, and when it does, you will notice it.
In the other functions, the sleep tracking is accurate, with minimal deviation from actual times. The heart rate, stress, etc. measurement seems okay.
The second major downside is in the mi fitness application on the phone (I have an iPhone 11), which unfortunately does not automatically synchronize with the watch even when connected via Bluetooth. You have to manually synchronize the data every time you open the application. For example, if you synchronize it at noon and then forget to do it at night, the application will not record the remaining data. And when the day changes, everything is reset on the band and you essentially lose the measurements that you did not synchronize in the application.
The battery life surprised me pleasantly, as with the use I make it lasts between 6-7 days without charging, with an average of 2-3 sports activities (soccer-airsoft) per week. I usually have Bluetooth turned off and notifications from the phone completely disabled. If you also turn off the heart rate measurement, then its autonomy will definitely increase more.
For those interested in running, the running function with the built-in GPS will cost you about 20%-25% battery per hour, but you will have slightly better accuracy in measurement than if you use the phone's GPS with Bluetooth connection.
In summary, with a cost of around 90 euros, I can say that it looks beautiful, performs quite well, and covers almost all the needs for which I bought it. Good battery life, relatively good calorie/step tracking, etc. The only negatives are the manual synchronization (perhaps not an issue on Android?) and mainly the non-functioning of the built-in GPS (and therefore the non-recording of kilometers) in activities other than running.