In combination with new gear oil, the gearbox became quieter and shifts gears more easily...

I have done about 500 kilometers after I put 2 tubes in a Seat Leon 1p tsi 1.8. I see a difference compared to before. I added it to relatively new gear oil, about 15,000 kilometers old. Time will tell, as I see it needs a period to do what it claims. For now, I am satisfied, there is a noticeable improvement.

Toyota Yaris MK1..1,300cc I put 1 piece. (It actually needed 2.) The gearbox shifted more smoothly, I recommend it. I kept it for 2 years, then I put new oil and a new additive, 2 pieces this time.

I used it in two cars:
Opel Corsa A 1.0 1989 200,000 km
I put it in as a precaution after changing to premium gear oil. After adding the product, I didn't like the gear changes and the gearbox didn't work as before. So I drained the gear oil again after about a week and then I noticed small pieces of metal. It seems that it caused a problem with the gearbox synchronizers.
Opel Corsa B 1.2 1997 320,000 km
I put it in because the gearbox bearings were making noise. The noise was reduced, but I haven't changed the gear oil yet to see their condition. However, based on what happened with the other car, I am afraid that similar wear may have occurred.
Conclusion: It may temporarily reduce noise, but in my experience it is likely to cause wear to the gearbox.
Personally, I would not use it again.
If you want to use a safe additive for the synchronizers, ProTec 2171 Easy Gear Lubricant 50ml is the best so far

It definitely does the job... Two mechanics have mentioned it to me... and I see it myself in a car over 20 years old... I have also used it in other private cars as well as in a commercial vehicle... for a period of over ten years... you feel the difference in the engagement and the feel of the gear lever, always in combination with good gear oils

Very good product, honestly for 5-6€/piece (in my case 2 pieces) you get a much, much better functioning of the gearbox. Let's not be crazy, it won't make it new, but the difference is noticeable. I had issues with 1st and 2nd gear when downshifting while moving, they would engage roughly and with slight scratching, as well as 3rd gear many times; now they engage more easily, and especially when the car warms up, it's like it has returned to its normal state again. PEUGEOT 107 2006 1.0cc

In a Hyundai Atos, it did an excellent job, not right away, but after 100-200 km. The 2nd gear was "scratching" and now it has stopped.. It needed 2.5 such packages, although I ended up using only 2 and it did quite a good job.

I saw improvement in the transmission; before it would engage first and sometimes third with a thud, now it does it rarely and only in first gear. The way I see it, I will take a while to lower the transmission; it has been given an extension of time.

Although I have bought it a while ago, I used it for the first time since then.

I used it in a Toyota Corolla with a 6-speed manual transmission and with 250,000 kilometers on the odometer.

What I notice is a softer and at the same time a nicer feeling in the car's gear shifts.

I haven't made any changes to the car's engine oil as I bought it used with the same engine oil that I bought the car with, and I simply poured this product in.

I haven't used it with new engine oil from the beginning.

As a first impression, it left me with a good impression.

I will come back in the future with updates.

I put it admittedly with some reservation, at first (and it is logical) I didn't see anything but after a few hundred kilometers I understood the substantial difference, the gearbox became a little tighter and the shifts more solid while it stopped a slight squeaking that I sometimes had when downshifting from 3rd to 2nd. Of course, I will put it again in the next oil change.

Overall, the transmission is more "tight" compared to most cars, but after adding it to the oils I changed, the gears shift more easily. I will use it again.

Problem with the gearbox in Opel Corsa d, it did an excellent job and the gears shifted very smoothly.

Immediately I noticed a sweeter performance and as the kilometers pass, I believe I will have even greater improvement!

I used it with Moly oil. Overall satisfied with the result but not sure how much of a significant role the additive played.