Use of solar reflecitve shades (harmful to windows?)?

We moved into a new house and they had some reflective shades installed to keep out the heat and glare. They are shiny on the sunny side and tinted on the inside. When trying them out they seem to work well at keeping out the heat and brightness but we have been told they are bad for dual pane windows. Supposedly the heat/light gets reflected back into the windows and causes damage. Is this true? Why would they sell them if they do this?