"Blue Devil" anyone heard of it

ok, have a 97 deville with a supposed blown headgasket that was given to me by my dad. changed out the thermostat already and went to change the radiator cap but the guy at the store said it is probably the headgasket b/c i can see bubbles and steam in the overflow tank. he handed me a bottle of "Blue Devil engine and cooling system fix all". pretty much, fix a headgasket in a can. anybody heard of this or tried it? 60 bucks for the bottle. wanted your guys opinions first. thanks