Not sure if this applied to Predator movies but usually a Hero prop is one that is showing in close-ups, and a Stunt when far away shots or when used in various combat and dangerous scenes or by stunts. A Hero prop has all the details, it is more fragile, sometimes comes with full electronics, lights, various effects. The Stunt is not so detailed, sometimes is just a pale comparison to the Hero since most of the time is shot from some distance. Stunts are also sometimes made of rubber, foam or wood to protect the actors. Hero and Stunt props were used in many movies and TV series like Star Wars, Stargate, Star Trek, Face Off etc.