Another special case where additives help: My elderly Yanmar (YM240) is from the final years of a 1970's or earlier design and was designed around the higher Cetane rating of fuel in Japan. It's natural for these early two cylinder thumpers to have diesel knock so severe you instinctively feel a rod will come through the block. CLANK CLANK CLANK. The racket is reduced some as it warms up but it still doesn't seem within reasonable limits. You couldn't sell a new model today that sounds so close to grenading.
Nevertheless this engine in the tractors and also used in semitrailer refrigeration units and fishing boats etc has a reputation for extremely long troublefree life. But I'll bet those Japanese fishermen are deaf.
I can't imagine staying below deck during rain in a small boat with that head-pounding racket.
It isn't the exhaust, its the steel in the block pounding like its being hit by a sledge. (
Example 1: vid with sound, somebody else's Yanmar, warm engine, without additives. Hear that sledge-on-anvil sound?
Example 2: Cold start, my YM240 with PS. Still primitive, but tamed some.)
There is a big, noticeable improvement running Power Service (silver) as a Cetane improver. It starts on the first cylinder to fire, with little smoke, and the diesel knock is half of what non-treated fuel sounds like as it warms up. Likewise lugging it down when warm does what it says on the bottle, avoids smoking and feels like it improves torque.
The other Yanmar (YM186D) is a more modern 3 cylinder design and Power Service slightly improves those characteristics, but it doesn't really need additives.
In summary I'm sold on the advantage of a Cetane improver, where needed. I doubt the brand name makes much difference.