As I read the study
1) They got to use some actual scanners (some other prior "studies" didn't).
2) Rapiscan (the equipment vendor) had advance knowledge of which scanners they would use, and controlled their access to the scanners. {As to why this is significant, do you think my local police would let me chose which of my guns they can test to match against the slug they dug out of a local homicide victim?}
3) According to the table on page 10, someone the size of a 10 year old child would receive a dose that's about 40% higher than the adult dose mentioned in the summary. Moreover, the dose they would receive in breast tissue is about 60% higher than the dose calculated for an adult.
4) This doesn't appear to be a peer reviewed publication.
5) As far as I'm aware, we still don't know what - if any - periodic maintenance or re-calibration work is done on these scanners.