Found this a bit confusing, but I did have a late night
Firstly, I thought the gist was that the bag rendered what was inside it invisible.
That would be quite scary.
Then I realised that it is the bag itself that is invisible to the scanners, therefore allowing unimpeded scans of the contents.
I'm not sure that this would meet with consistent treatment by security staff though. I can't see that the neoprene sleeve my netbook is in would hinder the scanners, but it always has to come out of the sleeve for screening at Manchester and LGW, although not at T5.