When he got back, Leo immediately went to his room. He felt so powerless when he saw the Magistrate look through him and Daphne in an instant. He didn't like that he would have to hide his power every time until he got stronger.
He was also lucky that he used a different Magic System. Otherwise, he would have had to explain to the Magistrate how he knew magic. It wasn't illegal for him to tell that he found a tome. Commoners were allowed to learn magic. If they got their hands on the magic.
However, the nobles control most of the sources of magic that very few commoners can actually learn magic. If Leo's tome was made public, on the other hand, he would be dissected and researched. He would be made an eternal slave for the knowledge in the tome. That was how valuable it was.