Reading the book, I understand that the author has excellent mastery of history but has little knowledge of Islam and the life of the Prophet (PBUH). He made some unsubstantiated remarks like "Muhammad (PBUH) was the wealthiest Quraish." At the same time, all the sources state that he was, at best, in the higher middle class, or "Muhammad (PBUH) married daughter of Abu Sufian (RA) for political reasons. At the same time, historically, it has no connection as history suggests that Abu Sufian did not get any help from Ramla bin Abu Sufian (RA) just before the victory of Makkah. He also made some comments that go against Islamic Shariah. For example, A Rahaman (RA) wore silk in Medina while it is prohibited in Islam for men to wear silk.
Even without considering those, this is a poor book, as I did not find a clear or substantial link between birth of capitalism and Islam rather I find interesting link on Islam and birth of taxation