I am in Missouri also and have seen these. I did not go this direction for exactly what Lefty wrote. At a marina you have to deal with spiders and it's not a tight fit and compared to other options it's not cheap. I think it's all in what you want. I can see why people would want them as who really likes covering their boat. I am religious with it but this would take away that element of boating.I looked at these and there are some where I am at at Lake of the Ozarks.
They offer protection from the elements but because they don't contact the boat, dirt and spiders can still get under the cover. I believe they are better than the std snap on cover.
I went with a cover by Marine Concepts. I believe they are only available in Missouri, Oklahoma and Florida. They are custom - they come out and digitize your boat and make the cover to fit. The cover rides on a track above the boat which you pull manually which I find easy to do and seals against the boat to insure it stays clean.