Just another way for GM to wrangle you to buy their products. As long as it is free I will use it. But, once I start paying for it I will change to a full synthetic. Is there that much difference? No I have had dang every kind oil I have used in my 8.1 engine in my RV analysed. All performed well. I even had Wal Mart oil tested in a Honda CRV with over 100,00 miles on it and it was good. You just had to change a bit more often.
The bottom line is how long will the additive package last?