Whew. Lots of info in this but it's basically like the green stuff in a bike tire...it gels up and blocks small passages to stop leaks. Problem is the whole radiator and heater core are small passages, so it severely limits the flow. It gets everywhere and you can't get it out. Basically ruins your cooling system. If you want to keep it in your truck in case your stranded and alone and have no other options, go for it but plan on replacing your radiator and heater core(s) when you get home, and know it will still probably be lining all thnme water jackets in your engine. Awful band-aid of a fix that has no place for a car of value.
EDIT: if you'd like to see what it does to a core tube, look it up on YouTube. You'll find a number of frustrated mechanics who cut open the junk radiators so people can see
Thanks for the explanation. Sounds like awesome stuff ....ugghh why would anyone keep selling it and not advertise the downsides?!? Never would have looked it up because it's so prevalent in all the stores.