When it comes to objectivity and justice, the authors of such books must not have a strong subjective color. They must objectively examine the Taiping Heavenly Kingdom as a special historical period with the method of historical materialism. A book like The Tragedy of Heaven won't work. Examples of relatively objective and fair books in this respect are as follows:

Chen (Japan) of Taiping Heavenly Kingdom

Taiping Heavenly Kingdom Data Collection compiled by Taiping Heavenly Kingdom History Museum

The Rise and Fall of Taiping Heavenly Kingdom Liu Renkun and Jia Cheng

Tianzi and his secular dynasty: Hong Xiuquan and Shi Jingsheng of Taiping Heavenly Kingdom (America)