I use it for every oil change on my Fiat Punto Evo diesel (change every 8,000 km) and I have noticed a better sound in the classic engine rattling and better rolling. It also seems that it hardly smokes at all, or definitely much less than the day I bought it second-hand.

Before I changed the oil, I used this specific product. I didn't notice any positive difference. The car then burned oil and I added 2 liters. In the next oil change I did, it burned oil again, which means that the product contains gasoline and cuts the oil. Logically, it held the oil pan and the old oil should be drained before putting in the new ones. I won't use it again. I prefer to use quality oils and change them more frequently.

The product does an amazing job. It takes half an hour before you need to change the oil, you put it in with a warm engine and after half an hour of the engine running, you will see the mess it will remove during the oil change.
I didn't have time to take a photo of the engine's interior from the top oil cap to show you how clean it became.
Oil and filter change is implied. And the engine will calm down significantly.

I bought it with reservations. Nevertheless, it seems to have done the job. The engine runs much quieter after the oil change!

Update
I tried it on another car, but this time I used different oils than the ones I used on the other car, and it really does a great job! Both of them work very smoothly!
Highly recommended!