It took us a few minutes to realize what Microsoft's new Arc Mouse is all about. The collapsible design at first suggested that it's both a full-size mouse and a notebook mouse in one product. We were confused as to who would want such a thing. Upon playing with it, we realized that there's actually some smarter design going on here. The unique shape and button-layout does present some usability issues, but overall, the $60 Arc Mouse may be the best solution for those looking for a full-size, travel-friendly mouse.
The benefit of the Arc Mouse is not that it works as a "notebook mouse" when you fold it in half. Indeed, the power to the mouse cuts out when it's folded, so it won't work in that mode at all. Instead, folding the Arc Mouse makes it more generally travel-friendly. First, it reduces the size of the device, cutting its length by more than a third. But there's also a small, magnetic cradle on the underside of the tail portion that folds in, to hold the mouse's thumbnail-size USB receiver. When the mouse is collapsed, the tail portion secures the receiver, ensuring that you'll have all of the necessary pieces together when you take the mouse out of your bag.
In its uncollapsed state, wherein you actually use the mouse, the Arc Mouse is not quite as clever. It works well-enough as a basic two-button scroll mouse, but the extra left-side button complicates things. If you hold a mouse in a standard grip, with your palm resting on the tail-edge, it becomes impossible for your thumb to reach the Arc Mouse's side button without contorting your hand. Situating your palm on the top of mouse (aka claw grip) solves the problem, but at the expense of precise cursor control. Holding the mouse thusly, we actually had to think about positioning the cursor over Windows' familiar close, "minimize," and "maximize" icons.
We agree that's a minor quibble. The side button isn't exactly crucial, and the core "mousing" functionality works as you'd expect it to. We also like that setting up the Arc Mouse is so simple. After you insert the three, Microsoft-provided AAA batteries, you plug in the USB receiver, wait for Windows to recognize the mouse, and reboot. Mac setup is even easier, as Mac OS X found the mouse as soon as we plugged the receiver in. For its intended purpose as a travel-friendly input device, the Arc Mouse does exactly what it's supposed to.