I use the Redline Water Wetter in my car... I noticed absolutely no subjective difference, but I have no objective measurement means other than the stock water temp gauge (which did not change after the addition of water wetter).
1) Open cap
2) Open foil wrap
3) dump into coolant tank.
Actually, if your coolant level is full when your car is completely cold, you need to siphon out the approximate contents of the Water Wetter bottle. Since I needed to top off my coolant anyway, I was good to go by just adding it in.