I've used it in 4 areas:
1. pour 9 oz in the crankcase and drive up to 100mi before an oil change as a sludge cleanse
2. funnel 1/3 of a can into the vacuum line to clean intake
3. add 1/3 of a can to gas tank as a fuel line and fuel rail and injector clean
4. I was getting low secondary air codes so I uncoupled the tube between the secondary air pump and the exhaust ports, filled the tube with Seafoam and had the pump blow Seafoam through the exhaust ports (only possible with a cold engine). Cleared the secondary air codes.
I rarely get any code, if I do I clear it with the Peake and it doesn't return. Car performs very well.