I just checked out the Xiaomi web site and looked at the watches. Excellent specs and a very reasonable price. I'm in the Garmin ecosystem for my running activities, they've been resting on their laurels lately and pushing up the prices to silly levels. Brands such as Xiaomi are underrated, they make good inexpensive phones too.
I moved from Garmin to Wahoo about 6 years ago and have been very pleased to date. My eight year old Garmin vivoactive HR eventually gave up the ghost a few weeks ago. The touch screen stopped responding. I've no complaints about that. My smart watch/fitness tracker needs are very simple and I set myself a budget of £150, which was far more than I really wanted to spend. Which? rated the Xiaomi Smart Band Pro 9 as "the best we have ever tested." Quite a glowing review. The watch is £62 and I decided it had to be worth a punt. I'm delighted. It does everything I need and about 429 other things!! Easy to use, smart looking, very responsive, comfortable and a lot of set up from the app. More setup from the app would be good but I can't complain at this price. My one gripe would be the lack of a decent manual but this seems to be a feature of Chinese/Japanese products - see my previous rants about Shimano. In common with Shimano di2 I had to use YouTube to find a good "how to" video.
Accuracy is very good. I've compared a medical grade BP/HR monitor, Wahoo chest strap and the watch. The strap and monitor are 100% while the watch is 1 or 2 beats out. That's more than acceptable. The vivoactive was usually 10 or 15 beats out. On walking and cycling the GPS tracking on a 75 mile ride my Wahoo and Xiaomi were within 0.11 miles and 19 feet of each other. The last thing I have to check is battery life for cycling. Currently it looks like about 22 hours for GPS tracking. As I only want it as backup on major events like the Fred Witton or Ride London that's more than adequate.
Highly recommended and I'll look at their phones the next time I need one. #2SP is waking, I had best go!!