The contacts get dirty, they dont fit some USB ports properly, they die regularly, are absolutely no good if you don't have a USB port handy (my desktop for example doesn't have a USB hole in the front or on the keyboard or monitor, resulting in crawling around under my desk to authenticate) and to be honest quite fragile.
All it does is act as a USB HID keyboard and pump some text down when you press the button on it. It's basically about as secure as an RSA key but requires physical electrical contact with the machine.
No thank you.
(For reference http://bigv.io/ uses these).