Leaving a window unprotected will allow most of the sun's rays to enter your home and radiate, the most efficient way to reduce heat in your home. Solar Screens can reduce up to 90% warming the temperature in your house. Stopping the suns ray's before they hit your window is of the sun's rays before they get to your house. This reduces the load on your air conditioner and reduces fading on upholstery and furniture.
The US Department of Energy states that exterior shading devices are about 50% more effective than internal devices at blocking solar heat. It has been stated that shading your windows and doors from the outside can reduce inside temperatures by as much as 20-30 degrees. Shading from the inside, such as tinting, shades or blinds will allow the heat to get inside your house. This will not produce as good of effect as exterior shading.
Installing a Solar Shade will allow you to see out and not allow your neighbors to see in. This statement is not true. These shades have a similar effect to one-way glass. They allow you to see from dark to light. Therefore, during the day you can see out but at night, with the lights on, people could see in.