This is a nice solution to wanting to use PS/2 devices (such as Adafruit's capacitive touch pad or magstripe readers). It's also handy if you want to connect a keyboard and mouse to a Raspberry Pi or Beagle Bone without taking up two USB ports. Inside is a full translation chip - a small USB microcontroller that will translate the PS/2 into "USB Keyboard" and "USB Mouse"
Adafruit tested this with a Pi, Bone, Linux, Windows and Mac desktop computer and they all worked flawlessly.
Total approximate length: 7 inches (178mm)
Cable length without connectors: 4 inches (102mm)