This thread from about nine months ago with good answers from u/schrodingers_lolcat and u/cleuseau discusses Florence's ban on Arabic numerals. Much as your author claims, Arabic numerals were banned for book keeping because of the ease of forgery. It was all Arabic numerals that were then allowed in the 15th century, zero included among them. Before then, at least in Florence, the preference was for Roman numerals, despite their inferiority compared to their Arabic counterparts.