Unexpectedly effective!
After about an hour of use, and 5-6 rinses, it still maintained its anti-fog protection.
However, be careful, the ingredients it contains are not for direct exposure to the eyes or inhalation. Follow the instructions that come with it.

Nah... it didn't work on swimming goggles.
I didn't try it on a diving mask.
Anyway, a better job can be done with an anti-fog marker!

It does a fantastic job. I use it on glasses that I had for a year and were getting blurry. It easily lasts for an hour, I have swum for up to 1.15 hours without any issues. I simply follow the instructions on the bottle

For 3 masks and goggles, 2 hours of swimming without fogging. Not even half has been consumed. I will buy it again when it runs out.

I have tried anti-fog mask spray from a total of 3 different companies and cressi's is by far the best. However, for the best possible result, I would recommend washing the mask's lenses well (once before the first use) with toothpaste and then, before each dive, leaving the anti-fog liquid inside the mask for 6-7 minutes on the lens before rinsing the mask to dive.

It does exactly what it says.
You spray it from a relative distance once to cover both lenses.
Then you rub it a little with your finger and let it dry.
Whether you clean it with a towel or wet the mask, it works with both methods.
How long it will last depends on each individual.
Certainly not less than 1 hour.

Sometimes it did its job, but most of the time it didn't. I tried all the application methods without anything changing

It's not worth a single euro. No matter how I applied it, it has no effect. Sometimes it holds for a few hours, sometimes it immediately fades

From one spray on each window, it definitely lasts for about 20 minutes, just wet your face before applying it

It helps a lot.... You spray it, leave it for a few minutes, dip the mask in water a couple of times, and you're ready.

I used it 5-10 times on brand new swimming goggles and there is no trace of fog. Without the liquid, the goggles fog up within the first 5 minutes. I spray a few minutes before use and rinse with water. One spray is enough for each lens. DO NOT spread with your finger to avoid scratching the lens (from dirt, salt, etc.). Highly recommended.

It does what it promises. I have it permanently inside my suit in case repeated spraying is needed, but generally it is not necessary.