5 stars for the job it does! After using a Garmin 5 that couldn't accurately track heart rate for any reason, I switched to the H10 and it truly follows heart rate fluctuations incredibly quickly in both aerobic and anaerobic weight training!

I use it on a daily basis in aerobic and anaerobic workouts. It connected seamlessly to my phone and my Garmin Forerunner 735xt. At first, I compared it to my Garmin and Polar during my workouts and I feel that it is more reliable. 4 out of 5 stars because once I tried to connect it to my phone after a workout and it wouldn't connect (eventually I deleted it from the app and reconnected it). Aside from this connectivity issue, the product is awesome and I recommend it.
Update. After 1 year of use, it still works perfectly, but it requires frequent battery changes. Other than that, I am satisfied.

For now, it works perfectly. It works perfectly with the Suunto 9 and also with the treadmill I have tested.
Update: I haven't seen a single spike. Literally!

Using two workouts (cycling and weights) seems very reliable to me. Easy to use and compatible with Garmin Instinct.

The only thing it cannot do is update.

Great accuracy in measurements, it has been used in various types of training without any slightest problem. It's worth its money, I believe, for someone who is looking for something good...

Amazing product, absolutely expensive and perfectly compatible with many applications of other manufacturers.

I have it paired with an iPhone 6s and it works with both Polar Beat and Runkeeper.
update: 08/05/2019
Note that it is Bluetooth and recognized by treadmills, etc.
Polar recently released a firmware update to enable ANT+, but I can't install it.
I continue to use it and consider it to be accurate, although the Garmin HRM RUN is now cheaper and offers more running dynamics.
Its main advantage is that it can track your heart rate without having your phone with you (with some limitations, of course)

Awesome tool for everyday training! Incredible accuracy in measurements!
It can stream live to your smartphone or tablet or to your Polar smartwatch through the free Polar Beat app! It also has the ability to upgrade its firmware through your mobile, which is amazing for future upgrades that enhance its functions! The belt provides excellent grip and a very comfortable fit, you forget you're wearing it! BEST VALUE FOR MONEY!! If you can afford an extra 25 euros, choose it over its predecessor, the H7, you won't regret it! Also, Polar has an online application that automatically stores your daily workouts, so you have a complete picture of what you've done daily for as long as you use it!