Review on KINGTOP Vertical Mouse Ergonomic Optical Wireless: Reduce Hand/Wrist Pain, 6 DPI Levels / 6 Buttons, Rechargeable for Notebook, PC, Laptop, Desktop by Sam Carter

The design is really innovative, but the product itself seemed unreliable and basically stopped working properly after a little over 3 months. The pointer moves out of sync and scrolls very slowly no matter how you set the DPI. Although it only costs around $26, you would expect it to last a little longer. 08/30/21: Added a star for quick customer service and replacement. Haven't tested a replacement yet, but this is for after-sales service.