This is a Logitech MX ERGO trackball, purchased around May 2025. I'm a trackball beginner, but it was very easy to use and allowed for a natural posture. It supports the FLOW feature, which allows you to connect to multiple Windows and Mac devices and easily copy and paste between them. I used it for about a week, but I'm selling it because it didn't suit my OS. It's in excellent condition with little use. Price is negotiable.