AFAIK, many states prohibit the use of radiation on people unless it's for medical purposes. I'm sure that someone will manage to get an exception for these types of machines given time. There are still ethical issues with exposing masses of people to radiation, no matter how low the dose. Most people are paranoid enough about radiation (mostly because of lack of knowledge). Now the TSA wants to unecessarily irradiating hundres of thousands of people with low, but not trivial radiation doses just to get on an airplane?
I smell much controversy coming up if the TSA gets their way with these units.