Energy film

The majority of our windows in the house are single pane glass. And with the windows being about 4'wx7'h, that's a lot of glass that is not that energy efficient. While the trees on our site protect most of the house from sun throughout the day, the low evening light does come through below the branches. We get amazing light in the house at those times of the day, but also some heat gain. I don't know what the winter condition is like yet, but I imagine the engery efficiency is pretty poor. Now with all the renovation that we've done, we are also pretty poor and can not afford to put in new windows at the moment. So I came across this product, energy-film.com.
Here is what they claim:
Energy Film is made of a spectrally selective material that blocks 70% of thermal solar energy in summer and reduces heat loss through windows in winter. It blocks 97% of UV light while still allowing 77% of natural light into the room. Energy film also has excellent visual clarity.

"An estimated $30 billion or more of Energy is lost per year through single pane windows"

"An average Home Loses 25% of Energy Through Windows"

I'm interested in trying this product out until we can afford new windows in the house. Anybody out there familiar with this product? How easy is it to install, does it work, do you notice the film?