The Logitech Ergo M575S is the current version of the M575, and it remains the cheapest sensible way into trackball use. The ball sits on the left side of the body and is moved with your thumb, so your hand and forearm stay still while the cursor travels across the screen. That removes the constant arm sweeping and wrist twisting of a standard mouse, which is why many people with sore wrists or shoulders try one.
A thumb trackball suits a particular kind of user. If you like the idea of a trackball but want something that feels close to a normal mouse, with a familiar left and right click under your fingers, this is the easiest transition. A finger-operated trackball, where the ball sits in the centre and you roll it with your fingertips, offers more precise control for design or spreadsheet work but takes longer to get used to. A vertical mouse keeps the pointer moving by arm movement, just with a handshake grip that eases forearm twisting, so it helps with posture but does not reduce arm travel the way a trackball does. The M575S sits in the middle: low learning curve, minimal arm movement, and a price that makes experimenting low risk.
It connects over Bluetooth Low Energy or the supplied Logi Bolt USB receiver, runs on a single AA battery, and works with Windows, macOS, Linux, ChromeOS and iPadOS. The shape is right-handed only, and there is no height or angle adjustment, so it is a simple, flat, comfortable design rather than a customisable one. Expect a few days of adjustment before thumb control feels natural, and a quick clean of the ball and its sockets every month or two to keep tracking smooth.
