That book is likely to be correct that it is a myth that "al-Andalus" was "a place where Muslims, Christians, and Jews lived in harmony" and that in reality being a non-Muslim must have caused many disadvantages.

Nevertheless, even without examining any evidence from that book, it is beyond any reasonable doubt that the non-Muslims had been much better treated under the Arab rulers than the non-Christians were treated after the territory had been reconquered by the Spanish kings.

For this, no other evidence is necessary beyond the fact that even if the non-Muslims might have not "lived in harmony", they certainly had lived there in great numbers, while soon after the reconquest the non-Christians no longer lived there (this is especially obvious from the large number of Sephardim who had to live in other countries after that).

Another thing that is true beyond any reasonable doubt is what is said in the parent article, i.e. that regardless whether the Arab conquest was good or bad for the local people, for Europe as a whole the Arab presence in Spain has been extremely useful, both as the source of improved knowledge in chemistry, mathematics and astronomy, due to their own research of various Arab and Muslim authors, and as the source of many ancient Latin and Greek works that had been lost in Europe.