anybody know if this will cause damage?

a freind of mine asked me if it was any good after he already put it in. Ive always been of the opinion you cant buy a mechanic in a can. anyone have success with this?

http://www.autobarn.net/blue-devil-engine-and-cooling-sealant.html

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1982 300CD Turbo (Otis, "ups & downs") parts for sale
2003 TJ with Hemi (to go anywhere, quickly) sold
2001 Excursion Powerstroke (to go dependably)
1970 Mustang 428SCJ (to go fast)
1962 Corvette LS1 (to go in style)
2001 Schwinn Grape Krate 10spd (if all else fails)