The added electronics just rest against the adapter's boards: http://samy.pl/keysweeper/testingsize.jpg. This looks quite unsafe because of reduced clearances. It has a chance of either exposing HV on the LV (USB power) side or shorting the various boards, potentially starting a fire.

It's a pretty cool proof-of-concept, but I wouldn't connect anything to the USB port. These issues could be solved for deployment by potting or by using a custom smaller PCB integrating the various boards.