What is the difference between an AKU and an AK0 reader?

Both AKU and AK0 readers have a USB cable, the difference is in how they communicate. AKU readers function as a keyboard and will output to any text field. Simply click your cursor into a text area such as word, scan a card, and you should get an output. AK0 readers on the other hand are virtual COM port readers and communicate with serial data. You would need to use a program that supports a serial connection like pcProx Config or a terminal application like Putty to see the card scan.