It depends who that person is and how much settled he is
in the faith of the Primal Vow. A person who really has faith in
Amida Buddha can read whatever he wants because he will never be
influenced by other religions, but someone not yet settled in faith
should better leave aside any nonBuddhist book and focus entirely
on listening deeply (reading is also listening) the Jodo Shinshu
teaching and asking questions to clear his doubts. Why? Because he
can be easily influenced by what he reads and everything he reads
can become an obstacle and make him depart from the Dharma and the
Primal Vow. I saw many people abandoning the Buddhist Path because
they read too many things.