Maybe nothing. I've used several Fram oil filters, 8 I think, but they just don't seem to be as well built as the Mann filters. I usually change the filter-only at between 5000 and 7000 miles, which gives me around 17,000 miles between changes. If I don't do that, it drops to about 12,000 or so. Once I didn't change is out at the 5000-7000 miles, and let it go to the 12,000 (or whenever it was the ASSYST told me to change it). I pulled out the Fram filter and it looked, and felt, like it was about to collapse and fall apart. I did that once or twice with the Mann filter and it came out looking "German Strong". I have a feeling that the STP filter is more like the Fram than the Mann.
But I know a lot of peopl use both the Fram and the STP filters. I'll probably use it when I change the oil tomorrow or the next day, then swap it out after 3000-5000 miles. It's basically a free oil filter with that deal, anyway.
With that special you're essentially getting a free oil filter and a free quart of oil, so it's worth stocking up for 2 or 3 oil changes, especially if you have the Autozone card where yuo get a point for every purchase of $20 or more, and then after 5 of those you get a $20 credit.
