The case handled here is different from the one I worked on. In my case the paint was completely gone through primer.
This approach would not have worked.
It's useful if the scratch is deep but have not gone through clear coat. By the way if you rewind my video, I did some wet sanding before using the Kizu Pen just to smooth out the surrounding area/paint. This way when the scratch is filled, it won't look bad. You can further wet sand or compound the filled area to improve its look further.
Remember touch up paint will never look 100% perfect. It will definitely improve the look, and it won't be noticeable if someone looks from a few feet distance. The purpose of touch up paint is to prevent rust and improve looks.
