Interesting
Yes, but I am not entirely sure why he elected to use HID as a serial device...
Going the HID route means the device will not appear as a standard serial COM port, so you can’t use the standard serial monitor to send and receive values.
Using keyboard HID allows debugging using and character capture device such as Notepad. My implementation examples based on rancidbacon's V-USB library:
String numeric output with V-USB HID - Exhibition / Gallery - Arduino Forum. It just seem if one is debugging, that a Java app just to mimic Notepad is a bit overkill.
The other concern is that the design calls for a 12 MHz xtal instead of the common 16MHz, so integrating with standard Arduino designs will require some additional changes in thee V-USB code.
I'm sure I am missing some hugely powerful benefit or something!
Ray B.