It is my understanding that these products have minimal, if any, effect on cars with coolant (ethylene glycol) in the cooling system.. from standard 50/50 concentration to even 70/30 coolant/water for very very cold climates.. however, in systems running 100% water, they have benefit.
Running 100% water in a cooling system even in a hot climate like Southern California or Texas still presents the need for rust to be controlled, and presents a rust issue.