I'll be first.
Got a Xiaomi Mi Watch recently as a present. Can say it looks very good, but it's a glorified smart band with a smartwatch screen. Basic stuff, no app store or anything. So tracking, weather, watch and music control functionalities, but nothing else. Also can't sync it with anything other than Strava (no Google Fit etc.). Software is also a bit off (Xiaomi...).
Says it holds up to 16 days on a single charge but that's also very hard. Most likely a week and a day or two, without the horrible, battery-draining Always-On Display.
Very grateful for it as a present, and at its price point (around 100€) I doubt you can do better.
For my money? Avoid. Work harder, buy a Garmin.