Is the car economizer useful?

It's no use. It is either useful or has a certain psychological comfort.

Tell you so, and you will understand everything. Look at the companies that produce and sell energy savers. One has made achievements in this field, one has accumulated decades of technology or experience, and even several have formal procedures, let alone qualifications. I'm too lazy to ask. If you think I am too old-fashioned, think again. The history of automobile development has been 100 years. During this period, many automobile manufacturers with top technology have made numerous breakthroughs in many fields of automobiles, but at present, even the efficiency of gasoline/diesel engines of these top automobile manufacturers can only be maintained above 30%, and no one can lead all the way. What is proved here is that technology is close to the limit. Every car factory spends tens of millions of dollars every year to study technologies to reduce fuel consumption. These cars have enough funds, enough technicians, enough theory and experience, enough test platforms and countless actual test parameters. They are all glad that they have reduced their fuel consumption by even 2% because of N improvements. What reason do you have to convince yourself that the fuel consumption problem of 120% can be easily solved with dozens or hundreds of products that are almost equivalent to cottage factories, and this technology is still available?

Fortunately, I am still open-minded, and it is too arbitrary for me to say that those things are not fuel-efficient at all. But the problem is that if it can't save money, it will lose money at most. If it is saved, it will sacrifice other performance and even cause other faults, which is a big drama. Because saving fuel is not the goal, but saving money, saving fuel and spending a lot of money in other places is unfair.