Cetane additive is really only beneficial when you’re going to be starting in very cold weather, or doing a lot of low lod and low rpm driving.
Generally speaking fuel with higher Cetane has lower BTU’s, and can actually decrease efficiency.
On my 05 when it was stock it hated Cetane and would knock with it. When it got new pistons and tuning it ran really well on Cetane boost, but I would only run it on ranks where I was going to do a lot of low rpm and low load driving, like elk hunting where I won’t break 20 mph for 300+ miles.
I haven’t ran it in my 18 yet, and likely won’t until Elk camp.
I do like to use a lubricity additive thou, and prefer Amsoil.