I managed to read the paper.
There are significant limitations to the study, and I agree fully that it is not possible to make sweeping generalisations as expensive running shoes are less useful or more useful than cheaper running shoes.
But there are some useful points. A shoe may not be safer or more useful because its RRP is higher than another model from the same manufacturer.
It is possible that more expensive models could be concentrating more on comfort which may not be related to shock or impact absorption.
Authors quote another study "Hazard of deceptive advertising of athletic footwear" which appeared on the same journal in 1997 which again suggest that expensive models does not always mean less injury.
Or somebody may have to come up with some thing like Euro NCAP's star ratings for new cars 