Eating less calories than your TDEE requires will result in weight loss. Eating more calories than your TDEE requires will result in weight gain. Only exercise will produce additional muscle mass.
So while a diet plan can help you lose weight, only exercise will get you “in shape”. When you lose weight, you lose both muscle and fat, you can work around the muscle loss by doing a few things; exercise, eating enough protein, and losing weight slowly 0.5-1 lb per/week (as opposed to quickly 2+ lbs per week). The problem with avoiding exercise and losing weight quickly is that you begin to develop the classic “skinny fat” body type. You also slow your metabolism more by not exercising and losing muscle.
Bottom line, will it work? Probably. However, it will also require that you exercise for best results. There aren’t any big secrets in the world of nutrition, and things are pretty straightforward generally. This plan along with countless others has the potential to help people, but it depends on the people themselves to make it work.