It cleans the fuel system, when it is inside the engine runs very smoothly (remains to be seen how it will work when it is not there).. I used it in two consecutive fill-ups because it seemed to me that when starting up it was running very rough. It smoothed out immediately. Its cost is reasonable and it's worth using every 5000km. I have tried other cleaners as well, this one seems to be the best of those I have tried

The use of it improves combustion, which can lead to better fuel efficiency and reduced emissions. At the same time, it can help smooth out engine operation, especially in cases where there are performance issues due to clogged or dirty injectors. It is easy to use, as it is simply added to the fuel tank before refueling.
Although it is a small 50ml container, this amount is sufficient for a complete cleaning process. However, repeated use may be required to achieve the best results, depending on the condition of the engine.
Overall, it is an effective additive that offers visible benefits regarding engine performance and the lifespan of injectors, especially in vehicles with high mileage or frequent use in challenging conditions.

I didn't see a noticeable difference, maybe a slight improvement but without showing over time.
Good for its price.

In a RENAULT 1.6dci every 4000km as a precaution. The 4 stars are because when you take it out, it gets stuck on the flap that the tank inlet has. In this particular car, I use a funnel to put it in.