1. Alja Safe alginate costs much less than Body Double silicone rubber. 

2. Alginate does not stick to anything. You don’t need a release cream for most applications. You can make a mold of the hair on your head with alginate by using hair conditioner as a release agent. You can’t make of mold of the hair on your head with Body Double. Best you can do is make a mold using a plastic bald cap.