The Gian Robert derailleur featured in this Ron Kitching advert is neither described in any detail nor depicted with any accuracy. But it is claimed to weigh only 4 ounces. As such it can only be the all plastic Gian Robert Campione model, with plastic knuckles, parallelogram plates, pulleys and even pulley cage plates. My example of this particular model weighs in at an astonishing 129g, including the hanger plate and bolt. This is about 4.55 ounces.
Many thanks to Andy Fraser for lending me this magazine and allowing me to scan it.