By Matthew Murray

No one expects computer hardware companies to once again make mice as boxy as in the early days of personal computing, but is it possible for some to take design innovation too far? The awkwardly designed new wireless Logitech Performance Mouse MX ($99.99 direct) uses Logitech'sDarkfield tracking technology to guarantee a smoothly moving pointer on any surface—even glass or highly reflective desks. And when it comes to basic functionality, the Performance Mouse MX lives up to expectations. But not all of its innovations are that successful—or desirable—for those who want an easy-to-point and easy-to-click mousing experience.

For starters, I found the button within the alcove in which my thumb is supposed to rest more a hindrance than a help. As the front of the mouse angles sharply to the left (thus ensuring that no non-righties need look twice at it), there's no alternative way to position your hand on it. Apply pressure in the wrong place or lift the mouse without thinking and you may accidentally click to open Logitech's Apple-like window-switcher app. In fairness, the function of this button, and the others on the mouse, can be changed using the included Logitech SetPoint software (though the customization options are less plentiful than you get with Microsoft's Intellipoint). Then again, the switcher is potentially handy and shouldn't be nearly so easy to unintentionally activate.

Slightly different trouble arises with the three other thumb buttons for forward, back, and zoom (for photos, used in conjunction with the scroll wheel). They're placed just out of reach of the thumb (or at least my thumb), which makes pushing them less than optimally comfortable. Button placement is, admittedly, a tricky science, but it's one Microsoft has mastered with, for instance, last year's Bluetrack-based Explorer, which requires fewer hand contortions to reach all the controls. (The forward, back, and task-switching buttons are more sensibly located even on this mouse's portable sibling, the Anywhere MX, which is also friendlier to the left-handed.)

The other controls essentially work as intended, though the scroll wheel's horizontal motion feels rather soft and unresponsive; thankfully, it's not as excessively clicky as with Microsoft's recent mice, but a middle ground would be ideal. A centrally placed button that adjusts the wheel's scrolling sensitivity can be useful if you prefer to scroll through documents quickly, but it may take you a while to get used to the difference between the modes. (The switching button itself barely feels like it does anything, but once you've pressed it, you'll note that the wheel no longer makes "clicking" sounds when used, and thus moves you around much faster.)

Otherwise, the Performance Mouse MX offers solid usability, moving with equal facility across surfaces as diverse as wood, metal, plastic, carpet, and the promised glass (something Bluetrack mice still have issues with). The 2.4-GHz USB wireless receiver is tiny (not even 0.75 inches in length), so be careful not to lose it, and it can also simultaneously drive a Logitech keyboard. (An extender cable is included in case you don't want to plug the receiver directly into a USB port, or your desk setup would make that difficult.) During my weeklong testing period, I didn't run out of juice on the included NiMH battery, but the mouse is easy to charge using the provided micro USB cable—one end of which plugs into the mouse, the other into either the included wall jack or a USB port on your PC. A stylish black carrying case simplifies carting everything around.

The attractive case definitely makes toting the Logitech Performance Mouse MX convenient whether you're headed to work, home, or somewhere in between. No matter where you are, the Darkfield technology lets the mouse work on most any surface. Whether you'll find the rest of the mouse as user-friendly depends on your tolerance for unusual design—if you're much of a traditionalist, this mouse could easily push too many of your buttons.