Since there have been so many prosecuted instances of men inappropriately using security cameras to view women's chests, cameras located in women's bathrooms, shoe and bag cameras to view under women's clothes, you know the jokers at the TSA will do the same. Therefore, unless the TSA can get real professionals into the job, it is a bad idea to give this capability to people very likely to abuse it.
Additionally, would this capability have detected anything a non-professional screener would have connected as being capable of being used as a terrorist tool ? I think not. TSA screeners are not hired for their background in the use of ordinary items as weapons.
This scanner is something every passenger would walk through.
The example I heard used recently is that it's not that difficult for someone to hide a quantity of explosives on themselves without them being visible under their clothes.
They might be discovered if every passenger was patted down, but are hard to detect by just looking at the person, and you don't need metallic items that would set off a metal detector to make a bomb.
However, a scanner that generally shows what is hidden under their clothes makes finding such items likely rather than unlikely.