I hate saggy boots, and I had high hopes for these boot stays.  They feel kind of like thin mini blinds that have been cut and wrapped in a thin cottony material.  When they are in boots, they are actually not uncomfortable - in fact, it's easy enough to forget about them.  I think that perhaps they would work better if they were a bit longer - these are only 6" long, so if you have more than a tiny bit of sag in your boots you'll need 2 pairs.  These work on mild sag, but I did find 2 pairs were needed to really keep my boots looking OK.  I have soft suede boots that probably need 3 pairs in order to really stay put.

The manufacturer recommends replacing these every 6-10 wearings, so these are not permanent solutions to your saggy boot problems.  I think they are a good idea, and I want to like them, but at $10 for 3 pairs and only 7" long, they just did not perform as I hoped.