Actually the Subaru additive does work WHEN USED PROPERLY. If you mix it with the wrong coolant, yes it will gunk up and cause problems. I myself have WITNESSED the additive work on a external coolant leak from a head gasket.
They WILL NOT correct an INTERNALLY LEAKING head gasket. This is the misconception that many have. These are two separate problems cause by two separate issues.
Subaru has taken responsibility for both issues. But bear in mind, how many car companies are going to cover a head gasket at 100,000 miles, your out of your mind.
My 2003 Baja's HG didnt go out until over 180,000 miles and I have had the coolant additive in my engine since the day they released it to thepublic. I have NEVER had an external leak.