3M Crystaline Window film vs Double Pane Windows

We looked at Cardinal FW late last spring. They had two rear living units, identical to each other with the exception of dual pane glass. One with and one without dual pane Windows. They were parked side by side with the rear window facing south. The unit with the dual pane had to be at least 10° cooler, if not more, and you could feel the a major temp difference at the glass. We were convinced right there our next unit will have dual pane windows.