Very satisfied overall with the purchase. Accurate, doesn't move from its position, and generally appears durable, although there are a couple of points that may make the experience disappointing:
1. The plastic membrane that touches the skin emits a slight rubbery smell that some may find annoying.
2. The Bluetooth connection can be problematic. It took me about 2 weeks to figure out what was happening because initially the connection kept dropping halfway and then it couldn't find it at all even if I cleaned the application and disconnected the device from the strap. Every time I used it, it asked to pair. The Polar-recommended apps (both of them) don't help at all in understanding the problem and they don't have any function to remove the device from the paired ones and start the process from scratch. For those who have similar problems, reset the device, remove all the devices that appear to be paired with your phone (I had paired the device 10 times with the same ID and obviously this confused the connection process later), and try pairing again from the beginning. If for any reason every time you wear it, it asks you to pair again, there is probably something left in the phone's memory (BT).

Since I solved the connection problems, it works flawlessly and reliably.

I was forced to buy it because my Garmin HRM Pro lost its waterproofing when I changed the battery and became unusable. I read great reviews and rushed to buy it. However, I don't see it surpassing the HRM Pro in accuracy. Also, every time I wore it in the pool, it failed to synchronize the data it recorded (if it recorded any) with my Garmin FR935 that I use. Additionally, no matter how tight I fastened it to my chest, it doesn't stay in place when changing direction in the pool and moves due to poor hydrodynamic resistance. I never had such issues with the HRM Pro, as its sensor is much smaller and has a rounded end so it doesn't create resistance in the water and doesn't move from its position on the chest!
Also, every time I don't use it, I have to disconnect the sensor from the strap because it "eats" the battery, as some users say, which reduces its usability... Washing the strap is not the main reason why one would need to remove the sensor, because if it is truly waterproof, there is no need to remove it at all.
It works fine in cycling, strength training, and treadmill with the Garmin FR935, but that's the easy part. However, in challenging situations (swimming), I don't see it being able to work at all...
For me, it is a useless purchase for now... Well, heaven forbid if I have to buy a Polar watch to be able to track heart rate during swimming. I give it three stars for now...

I am completely satisfied.
For many years, I have been using the Polar FT7 watch with the chest strap and H1 transmitter (which does not have Bluetooth connectivity) that accompanied it.
The H10, in addition to Bluetooth connectivity, comes with an excellent chest strap, fully compatible/interchangeable with those of the FT7.
In normal workouts up to 145 beats per minute, there is no difference compared to the cheaper Polar FT7/H1.
The difference becomes apparent at high heart rates above 160 beats per minute, in speed running workouts where the H10, compared to the Polar FT7/H1, shows 5-8 fewer heartbeats.
This may be happening because the chest strap of the H10 does not move on the chest during intense workouts (perhaps the higher heartbeats of the FT7/H1 are due to false readings from movements).
My only concern is how long the excellent chest strap will last, as its price is quite high.

Update 12/4/2023:
After 4 months of intensive use:
The strap (chest strap) after about 3 months of use continues to function correctly, HOWEVER: the elastic part (black rubber?) that comes into contact with the skin starts to harden noticeably and smells like burnt bakelite, and after 4+ months, it has hardened even more. Unfortunately, it creates horizontal scratches on the chest. With the intense sweating caused by running, the human skin softens and is easily injured by the strap that has hardened. The sensor has no problem - I have changed the battery once in 4 months.

I have been using the zone for over a year, I use it almost every day, I am very satisfied with the quality and reliability of Polar! If you want a heart rate monitor, it's a one-way street. Very good application, it doesn't move from its position at all. I have used it in the sea for swimming and the measurements were accurate, it doesn't lose anywhere. I use it with the Polar applications, Polar Beat and Polar Flow. It takes a CR2025 battery, which has a lifespan of about 1 month with 5-7 days of use per week, from 1 to 2 hours per day. I bought it for 95€ and I have no regrets at all! The least I can give is 5 stars! You can call it a teammate..

Well, after 1 year and about 6 months, I had to change the strap because it started showing inaccurate readings. The transmitter hasn't had any issues so far. The strap costs 50 euros. Specifically, they told me if I want to use a strap from H9, which costs 30 euros, or use the H10 strap again, which costs 50 euros, as I mentioned above. I asked the representative what the difference is, and he replied that you get what you pay for.

Comparison with Garmin heart rate monitors:

(+) The major advantage of Polar is that the heart rate monitor is detachable, so you can safely wash the strap. On the other hand, Garmin's heart rate monitor is integrated into the strap, so no matter how careful you are when washing it by hand, it will eventually get wet and break.

(++) Polar has a much more comfortable fit. Garmin's strap loosens after a few workouts and needs readjustment.

(+++) It has fairly good accuracy in heart rate measurement. However, I have noticed that sometimes, at the beginning of my workout, it keeps my heart rate steady at 70 beats per minute and then jumps to 120-130 beats per minute after 3 minutes of running. This only happens with this strap. Conversely, Garmin's strap sometimes gets confused when I have connected my phone, strap, and watch together and shows 250 beats per minute even though I haven't started running yet. Even when I completely remove it, it still shows the same reading.

(-) It connects to Garmin watches instantly, but it doesn't provide any other information on Garmin Connect besides heart rate. On the other hand, Garmin's straps excel in this aspect by giving you a complete analysis of your workout through Garmin Connect.

Having tried both (and for a considerable amount of time), I can confidently say that I prefer Polar

Buy it with your eyes closed!
Extremely accurate measurements! Easy connection with your mobile and the Polar Beat app. The strap connects with ANT+ and Bluetooth (with two devices simultaneously, e.g. mobile and treadmill or ergometers). It remains stable in its position even with intense sweating. One negative aspect is that it doesn't have GPS and you need to use it in combination with a sports watch or carry your mobile with you when you go for a run (if you want to track distance, elevation changes). If you simply want to track your heart rate and zones, you can use it independently, without a mobile or watch. You open the app, choose the workout you want to do, leave your mobile at home, and start running/doing another workout. As soon as you finish, the strap synchronizes with your mobile and you can see the results. But you're running blindly... A major drawback, but the truth is that it doesn't personally affect me because I use it with my Fenix. On the other hand... it does the same job as a Garmin Hrm (which costs half the price). It just has slightly better accuracy in measurements and never "loses" you.
Personally, I got it for its exceptional build quality (the Garmin HRM fell apart within 6 months with 2 hours of use per day. It was heavy use, of course, but I expected something better from Garmin). So far, with the exact same use and almost the same period of time, the H10 is like new!!! Especially its electrodes (see photo). It's as if it was never worn.