I am not a big fan of Auto-Rx, but it is completely safe to use in all diesel and petrol engines. I personally used it in a small common rail Mercedes engine, and it did nothing bad to this one.
In some engines, particularly if you haven't been using TRUE synthetic oil(group 4 or better), it can do something good.
The esters in the Auto-Rx, will enhance the lubricity in most oils.
It will most probably also do some cleaning, but there are better products out there.
It can be hard to find, though.
DieselTech says that all additives are the same, and that is simply NOT TRUE.
He just won't tell you that he has no clue about additives, and the safest thing for him to do, is to stay away from all of them.
I can understand his reasoning, but it doesn't make it more correct.
Some of his oil choices, are very good, though.
But, not necessary if you use the right additives