Lol! Well if you want to know what the guy who invented them and has been selling them for 28 years has to say, you came to the right place. As long as your pump falls within the depth and pressure requirements for the CSV, there really are no cons. As a matter of fact just the opposite is true. The CSV really does make pumps last longer and use smaller pressure tanks. It also solves a lot of other problems that are known to be caused by cycling the pump on and off too much. Like you said, with a good well and a good submersible pump, most people don't have a lot of problems with the old pressure tank method of control. The CSV utilizes that same old dependable pressure tank control, and makes it even more dependable. Eliminating the cycling is about the only way to improve upon that old tried and true pressure tank method, and that is what a CSV does. Eliminating the cycling makes the pump, tank, pressure switch, control box, check valve, and everything else in a pump system last longer. It is like starting your car engine a couple times a day compared to a hundred times per day. Of course you will also have to learn to live with a strong constant 50 PSI in the shower compared to the old 40 to 60 swing over and over. Most people say they no longer even need soap with the constant pressure being so strong.
If you had rather hear from five or six hundred people who have a CSV at their house, just follow this link.
https://cyclestopvalves.com/pages/reviews