I have a Xiaomi Mi Band 1, 3, and 4.
I use my Mi Band 3 only. It has the best battery life, while also having a clock display.
I don't need the Mi Band 4, as my Mi Band 3 already does everything I need. Clock, stopwatch, countdown timer, and is the most comfortable of all.
Before 2020/feb, battery life was around 31-31d on average. Since that, battery life has been ~42d on average. That is measured from 100% charge to 1%.
I only have a smartphone for the convenience of looking up prices, public transport time table, pathfinding, phone stuff (calls, SMS), and internet chat, and I actually hate using it, so having a dedicated watch is extremely convenient for me personally.
I also prefer my Mi Band 3 over regular watches, as I grew up with 24hr clocks from birth, and I also like that it can display date as well, not only time. It also works in the dark.