Interesting post here. Yes, I get that are selling something:
https://blog.amsoil.com/what-is-cetane-and-why-does-it-matter
I have used the following since I bought the car almost 2 years ago. Absoluetly no smoke and my tail pipes are completely clean. No black soot or anything. They are just silver coloured the way they were made. It cleans and also increases Cetane levels. Don't OD since too much Ceatne is not good!
On my last MOT the guy (who I know) said that my emissions were very low for a diesel. Happy Days.