The first bullet basically says the same thing as the 2nd one; I left it out because I felt it was redundant, not to mislead. If I wanted to mislead, I wouldn't have linked to the manual.
I think most additives don't hurt anything, and as I said in my post, I have run a number of additives in the past. It has been my experience, however, that they don't appear to do anything besides un-gelling of fuel (which is a valid use).
The synthetic tests of additives aren't necessarily directly applicable to how they help our fuel system life. You can increase MPG slightly with an additive (by effectively altering combustion speed/timing), though that effect is lower with a good mileage tune in the truck. In my case, when I calculated the increase in MPG and added in the cost of the additive, there was no cost savings per mile. Consider the fact that the majority of diesel owners don't use an additive and see the same injector life as those who do.
These are the reasons I
personally don't use an additive. As for GM's reasons, this is the latest bulletin I could find, from August 2016:
3-06-04-017I
It goes on to explain that the main concern is with water emulsifiers (most modern diesel additives don't do this), but the key takeaways are an additive is not necessary, and additives can't fix poor quality fuel.
So I will stick with my original advice: run good quality diesel, and don't bother with an additive.