This is one of the selling points of some screen shops and in my opinion is simply a sales line. Solar screens do help shade the window but they are still a “partial” shade. As long as some sun is still hitting the glass the amount of heat radiating through the window frame is negligible. The real problem is solar energy easily penetrates the glass and then the resulting heat is trapped inside. All focus should be on shading the glass, and until all the direct rays are completely blocked the thermal conductivity of the frame is a non-issue. Windows will never insulate like a wall, but shading the glass from direct sun can significantly reduce your cooling costs.