I don't know why there are so many good reviews. Even if the iron is rusty, in the places where there is no rust (e.g. if we scrape more with the wire brush) it does not react and does almost nothing. I am attaching a photo. I painted with two coats. However, the metal (a pin from a knob) was dull and not rusty, and I had removed the rust with hydrochloric acid. As an experiment, I stuck adhesive tape and pulled it off abruptly. Both layers came off very easily. So, the same will happen with impacts and scratches. I am almost sure that even on rust it will protect somewhat superficially, but it will come off easily with impacts, scratches, and adhesive tapes. On rust, it blackens more.
As the following video also mentions, most rust converters are not 100% acid, e.g. tannic, so that a reduction reaction with iron oxide occurs. This particular one is something organic, maybe acrylic paint, and they add a bit of phosphoric acid inside to create the blackening. Acrylic paint is inferior to epoxy paint on metals. Thus, you don't need to neutralize the acid afterwards to apply the primer or paint.

https://m.youtube.com/watch?v=tu1n1POMg98&pp=ygUOcnVzdCBjb252ZXJ0ZXI%3D

Because I have used this and similar products many times, I have the following advice:
1. First, we scrape off the thick rust.
2. We mix very well, very well. What the friend below wrote about the pebbles is a very good idea.
3. We put as much as we think we will need in another PLASTIC cup so that we do not dip the brush we are painting with into the bottle of the packaging and destroy all the material. Even the small amount of rust on the brush will ruin it all.
4. We paint two coats.
5. When it dries, we paint 1-2 coats with paint to cover it, not with a mini, paint to close the pores.
These materials "plasticize" the rust in a way, but they do not last long if we leave them exposed, moisture passes through and it starts all over again.
Why do I recommend it?
Because no matter how well someone tries to remove the rust from the iron, there is always a high chance of leaving some "roots" behind, resulting in it continuing to work under the paint.
By "plasticizing" it with these materials (whatever brand you choose), you eliminate this possibility.