The point at issue here is the total contrast between Herodotus and the Persian/Egyptian sources. There is further "pro-Egyptian" evidence:
See website http://www.the-persians.co.uk/cambyses.htm
Discussion: do the students know of any other figures (real or historical) about which such conflicting opinions are held?
Opportunity for imaginative writing from perspective of a Persian soldier in Cambyses' army marching into the desert.