I'm here to save you all with my ownership experience. I have one of these through a bluetooth mouse and keyboard deal Motorola held many months back. The mouse pairs through bluetooth to any bluetooth device (even android phones!) and the size is pretty much perfect, although I'd personally like it to be a little bit bigger. It fits in the credit card sized MP3 player pocket in my backpack, so it really is small (remember those are AAA batteries that it's next to). I've never had to replace batteries yet, but when I do, I have some AAA sanyo eneloops set aside for it. Dust doesn't get into the grooves, but I'm a generally clean person, so I can't say much for people running from airport to airport using it on every surface known to man. Those grooves actually give the device a nice grip, and don't feel like I'm holding a lubricated pear that's trying to run away. The only real downside to me is the lack of back and forward buttons, the lack of sideways scroll wheel movement (almost all mice lack this, but not my Logitech G5), the fact that the mouse feet on the bottom are a little thin and might wear through quickly, and the fact that I'd like this to be a little bit bigger.
If you're between this little guy and a logitech one with a USB dongle, go bluetooth! If you want a small bluetooth dongle, you can buy one and then reap all the benefits of pairing with other bluetooth devices. If you have built-in bluetooth, you won't need one at all! It's much better than having to use up a USB port every time.
Note - The one in the picture is not broken, I'm afraid that the staff put the battery door (which is also the mouse buttons and entire top body) on, but missed the right side clip that slips into the frame. the battery compartment is actually pretty nice, the two front clips slip into place, and the back is magnetic and locks itself in. To remove it, you just pull up the back with your nail.
Note 2 - Ah what the hell! In for 3!