The sound quality is different when the active noise cancelling is turned off. Additionally, I don't know if it happened to me, but the right channel has a smaller frequency range. It means that it reproduces certain frequencies with lower intensity compared to the left channel, especially the bass.
One solution is to use a stereo graphic equalizer application on your computer or mobile device (separate for each channel) and adjust the volume for your preferred frequencies.
Apart from that, it satisfactorily isolates external ambient noise.
UPDATE November 29, 2021:
After some time, the symmetry in frequency response improved in both channels, surprisingly.
BUT, because I didn't use them for a long time, meaning not more than an hour, everything was fine.
But gradually, especially when approaching 2 and 3 hours of use, they started to slightly bother me in certain areas around the ears. I wish they had a larger diameter. They are narrow. Maybe if they were round, they wouldn't bother the ears after prolonged use. It also depends on the size of your ears. If you have slightly larger ears, they are not for you. :-)
Also, you need to find the ideal position every time you put them in your ears; otherwise, when the active noise cancellation is activated, it creates a buzz. It can be corrected by slightly adjusting them on your head to a different position. I don't know if it happened with mine or if it's a general issue with the Platinet ZEN FH0930AG model.
One of the reasons I bought them was to use them as ear protectors when I'm bothered by machines or when some neighbors make noise (vacuums, loud TVs during quiet hours, etc.).
Today, I might have bought the Mpow H12 IPO Black, which is cheaper. There are plenty of reviews on YouTube about them.
If you're more picky, you can go for the more expensive ones.
UPDATE: When I wrote the post, the Mpow H12 IPO Black was cheaper. Now, on May 22, 2022, they are more expensive.
UPDATE 2: They broke after an accident in late 2022. I bought another pair in January 2023, the TRACER STILLO ANC BT from a well-known e-shop for 20 euros. They are great and don't have any issues with ANC (Active Noise Cancellation). It seems like my ears have grown fond of them, and they are comfortable to wear.