Shrink to fit winter windows are really great draft stoppers and energy savers for old windows and patio doors.
Plastic has almost no R-value
Since plastic and glass have no real R-value, the dead air space created between the plastic and the window is as good as can be created with another pane of glass, so your double windows are now triple windows.
As well, whenever windows are imperfect, the best air seal should be on the inside and the leakiest on the outside, that will keep the windows clear of condensation. The reality is that if you apply the tape and the shrink wrap plastic with care, you can make this inside pane almost perfect.
Another reason that these windows work so well is that they end up flush with the wall so that the air from the heating system flows right over the plastic surface, keeping it condensation free.
Tricks to a good installation
Do not try to install the tape on the inside frame of the window near the glass, it will tend to pull away from the wall here. Install the tape on the outside edge of the window trim if possible as in the first photo above. This way the plastic pulls around the corner of the trim, giving the tape much more holding power.
Where you need to work around curtain fixtures, tape diagonally across the corner of the trim, forcing the tape all the way into any curves in the molding.
You will have to mess around a bit with complicated corners like with the window sill.
Start your plastic on the top in the centre and work to each side, then down, pulling it as tightly as reasonable for the instant. There will be wrinkles, especially in complicated not flat corners.
You will be amazed at the ability of this stuff to shrink and totally eliminate all the creases except the fold marks, which come out a few weeks later. Just keep playing your hair dryer over it, moving back and fourth on the high heat setting. It is easiest to do this on a non-windy day, but you can come back later if it appears to have gone slack.
Simply take a razor blade or sharp knife and cut off the excess plastic beyond the tape. You can actually use these plastic sheets year after year. The only catch is that you will need to put them on a smaller window each year, because you just shrank it. So organize it to move them from the patio door to the big windows to the small windows each year and it will cost you much less to keep the drafts out.