First time fitness band user, former owner of two Garmin Forerunner models and a Samsung watch, I decided to go for something simpler in appearance so that I can also wear one of my regular watches from my collection at the same time (I mention this to show that I have some experience with such watches in order to make the comparison). I regretted it deeply. Wearing it constantly to count my daily steps, it counted... the movements of the hand I was wearing it on. And if you're a person who expresses themselves by vigorously waving your arms like me, it might show that you took 3500 steps... while sitting in a café chair!!! The same goes for sleep tracking, the two nights I used it, in the morning when I got out of bed... I had taken 1900 steps... I wasn't even sleepwalking. The accuracy of the GPS did not satisfy me, without being able to judge it completely. The one time I used it for a 2-hour, 9 km walk on the banks of the Pineios River (I live in Larissa), it showed that I was walking... in the middle of the river (when I transferred the data to Huawei Health), even though the paths are more than 20-50 meters away from the bank. I couldn't verify the accuracy of heart rate measurement. On the second day, it went back in the box for sale!

I bought this watch mainly to track my swimming workouts, so my review mainly focuses on its performance in this area. Its performance in swimming workouts is purely disappointing.
First of all, even though I swim almost the same route along the beach every day, it never recognizes the exact distance I swam. The watch itself, during the workout, shows completely inaccurate swimming distance and calorie consumption. It usually falls short or goes over by half a kilometer. In fact, there have been times when it showed that I swam 88 kilometers in a 45-minute period! On the route it shows me on the mobile app (after the workout, through the Huawei Health app), it shows that I made zigzags (while I was swimming straight along the beach), and many times it shows that I was swimming on land! So, the GPS is a disaster, at least in the sea.
Furthermore, sometimes during swimming, the watch stops tracking my workout, and the measurement up to that point is lost, as if I never started a workout (even though I had properly pressed the start of the workout and it had started measuring). And when I connect it to the Huawei Health app, it's as if I never started a workout.
During my workout, I swim all swimming styles (freestyle, breaststroke, backstroke, and butterfly), following a specific program. However, when I connect the watch to the Huawei Health app on my phone, it doesn't tell me which style I swam, nor the distance I covered in each style, nor the calories burned in each style. It simply says "Mixed" swimming style and calculates all the calories together.
The watch's screen locks as soon as I press the start of swimming, and it is very difficult to operate the watch in the water or with wet hands. Therefore, even if I wanted to track each swimming style separately (by ending the workout on the watch for the previous style and starting a new workout on the watch for the next style), it would be extremely difficult or almost impossible, as dry hands are needed to operate the watch's screen (which I think is a disadvantage of all touch screen watches).
The battery life, with daily workouts of 40-50 minutes and sleep tracking, is 3 to 4 days. If you stop sleep tracking, the battery lasts a little longer.
As mentioned above, I bought this watch mainly for tracking my swimming workouts in the sea, and I regret it, as it has absolutely no accuracy in its measurements, neither in swimming styles, nor in distances, nor in routes, nor in calorie consumption. Under these observations, I would have preferred to buy a simple waterproof watch at a much lower price, with which I could simply see the time while swimming. The Huawei Band 4 Pro offers me nothing more. Additionally, I can measure the distance I swim on my computer myself, using Google Maps, with infinitely greater accuracy than this watch. And there are websites on the internet that also calculate calorie consumption for specific swimming distances, without the need to wear a watch that offers absolutely nothing in measuring swimming workouts.
In the positives of the watch, first of all, it is beautiful and stylish, and its screen is bright enough even under the strong sunlight at the beach. Additionally, a positive aspect is that it has an oximeter, meaning it can measure the oxygen level in the blood as well as the pulse rate, although Huawei emphasizes in the instructions that this watch is not a medical device, and one should not rely on its measurements for medical purposes. Another positive aspect is that if the battery runs out during a workout and the watch turns off, the workout data until the moment of the watch's shutdown is not lost, but when the watch is charged and connected to the mobile and Huawei Health, this data appears in the Huawei Health application.
In the few times I used it for walking, it seems to have better measurements for distance and calorie consumption. However, for walking, there are plenty of applications for mobile phones, and I don't think anyone needs to buy a separate watch to measure walking. I have not used the watch for other sports activities, so I cannot know its performance in measuring the training of other sports.
For measuring swimming training, I think it definitely needs firmware improvement, so that this measurement can be improved.

Update 28/7/2020:
About 2-3 weeks ago, there was a firmware update for the watch. I don't think I saw any improvement in swimming measurement. The workout measurements remain extremely inaccurate and unreliable. Additionally, the GPS is still highly inaccurate, showing that I am swimming even on land, or that I am zigzagging (while swimming straight), or that I finished the workout in a completely different location.
However, the most significant problem with the watch (regarding swimming) I think is that it loses the measurements, as I mentioned above. That is, while I start the workout on the watch normally, there are times when I go to check the measurement during the workout, and the workout measurement has disappeared. This problem happens many times even at the end of the workout: often, as soon as I finish the workout and while I see the total workout time still counting, I go to unlock the screen to press "Stop" for the measurement. Then, many times, the screen goes black for 2-3 seconds, and then the measurement has disappeared. And then, no element of my workout is transferred to the mobile, as if I had never started the workout on the watch.
Now, for the positives of the watch: If someone starts a workout and swims only one swimming style, the watch understands which style it was. However, as mentioned before, using the watch's screen in the sea is very difficult to impossible. Also, I think the battery performance of the watch has improved. And finally, the sleep quality measurement is quite useful.

Update 1/9/2020:
I have stopped using this watch to measure my swimming training in the sea. Its measurements are either completely invalid or suddenly disappear during the workout. I only use it to see the time during the workout. This watch was one of the most unsuccessful purchases I have made! With this money, I could have bought a classic waterproof watch, which wouldn't require charging every now and then.