It's smart for a couple reasons. Of course, the concept is simple: trap the air between the glass and the room and the air becomes the insulator. But it's all in the implementation and that's where this product shines. It uses double-sided tape that isn't so sticky that it will pull of paint when removed. Have to get that right and they did. The real attention to detail is the film material. When installed, it better not look tacky. So they formulated the material to shrink just enough to tighten it up to pull out the hard and soft wrinkles, but not pull away from the tape! Don't worry if the tape and the film lie on perpendicular planes. The film won't pull off when it shrinks. It's resilient enough not to overcome the film-to-tape adhesion. Again: brilliant.
It is also optically clear, not at all diffusive. That is another absolute must. I was simply amazed at how this product brings all this together into a cheap, effective solution to drafty old windows. Someone reviewed that the tape wouldn't stick to their window frame. Probably a surface prep issue. In my application the paint was new and firmly bonded. I even had strongly curved surfaces to tape over. I found that heating the tape with a hair dryer helped conform it to those surfaces. Directions don't address that issue and for flat surfaces it's not one. This is a great product!