There's literally a whole section on glass coatings. But he makes the point fairly reasonably that in large parts of the world the climate is extremely seasonal and so you don't necessarily want glass coatings because they affect the glass all year round. Is a good point really perhaps you live in a temperate climate and so are not as cognizant of this.

The curtains bit is especially stupid because obviously curtains heat up and then radiate that heat back into the room so no they don't block heat they block light. If you want it to be dark then you have curtains if you want it to be cool they don't do anything.