The review is exclusively for the 2 main reasons I bought it, mentioning its positives as well.
I bought the Amazfit GTR4 from the official company store (at a significantly higher price than independent importers, mainly due to the official warranty) to replace a 4-5-year-old smartwatch from another major Chinese company, which no longer connects to GPS (it broke on the smartwatch, firmware issue, no longer compatible with the app that has been removed from the Google Play Store, although supported by Gallery/incompatibility with Android???).
The 2 main purposes are (a) when I swim (only now) in the sea ~2km at a time (35'-40'), day after day (weather permitting), 12 months a year and I want to periodically monitor the data (exact distance, pace, and especially heart rate) and (b) to quickly answer calls when I don't have my phone with me, while driving... The evaluation is therefore inevitable, both generally and specifically, in comparison to the previous one for the main purposes.
Pros:
1. Excellent XiaomiStore support! I sent an email with questions and received a response in 1 hour and 40 minutes.
2. Excellent GPS, much better than my previous one (2 satellites). Very accurate, with many settings, 6 satellites, etc.
3. Equally easy and comprehensive mobile application (Zepp), very good UI, plenty of features, settings, information... However, be careful: If there is a pending update, the application does not open/crashes until it is updated.
4. The usual battery life for all Chinese smartwatches (1 to 2 weeks depending).
5. Much lighter.
6. Reasonable price (200-250€).
Cons:
1. The strap is mediocre at best. In the summer, the wrist sweats more because it does not have holes along its entire length.
2. Very few/less faces and generally average for my taste. Fortunately, there is the AmazFaces app (Ukrainian and so we can support them through the ads that only appear when we download), with almost all faces available for free.
3. The heart rate monitoring intervals (BPM) are at least 1 minute, not continuous like my previous one. A big difference for someone who has a reason to monitor them continuously/real-time.
Now, for the 2 main requirements:
4. The heart rate sensor and/or algorithm are completely unacceptable for swimming! (on land, e.g. walking, it is very accurate). While I know that under normal swimming conditions, my heart rate is 100-120 depending on the weather conditions (measured at the carotid artery for 15"*4=1' but also from the previous smartwatch), the AmazFit shows an average of 167 with a max of 197 (see photo)!!! It's impossible, because my swimming pace is slow, and even if I could swim for that long with that heart rate, I would have either stopped reflexively or literally died (roughly, the maximum heart rate is 220-age, so for my case, 220-63=157)! Of course, I cleaned the sensor, tightened the strap as much as possible, but no difference. I did 3 tests with the same results.
5. When there is an incoming call (requires a special Bluetooth connection to the application), the caller's voice is not audible at all, and my voice is very faint to them. I went to the Mi Store and tested it with a connection to another Android phone (not Xiaomi), and it sounded fine. So it wasn't defective. They told me that there is a known issue with Oneplus (I have the 10pro and also the older 7T, with the same problem).
Of course, I sent all the data for the heart rate and calls to Xiaomi, through the application, to see if and when they do something. For now, I got it unfairly.
Conclusions:
1. Xiaomi, obviously to beat the competition, did not test the functions sufficiently, either in all the exercises they support or if it connects correctly with all mobile brands (OnePlus/Oppo is not, for example, Samsung, iPhone but also not, for example, Fairphone, Nothing, it has a significant market share).
2. If you have more "specialized" requirements like me, do not buy it. Get something cheaper, depending on what you value more (for example, a band with 40-50 €, they exist).