1 in terms of price and quality, Mi Band 4 is an almost flawless gadget. 2 it is very light and almost not felt on the arm. 3 can do everything that more expensive models can do: notifies about SMS, calls and messages on Facebook, Twitter. 4 protected from water (just do not dive). 5 this smart watch has a built-in heart rate monitor with the ability to constantly measure your heart rate, monitor your sleep, the number of calories burned and steps taken, as well as the level of physical activity