it says 5-15 degrees cooler.........that aint much....not for 2 slots!
i got 10 degrees cooler adding a thermal exhaust fan single pci slot thingy, quite neat, only cost a couple of quid too.....at first it was only a couple degrees cooler, but i opened the front flap covering the front USB ports (Dell 8400 Dimension) and it seemed to allow better airflow.....