What is your opinion of the book "Musnad Al-Sarraj"?

Musnad al-Sarraj is the Musnad of Imam Muhammad ibn Ishaq al-Thaqafi al-Naysaburi, one of the great hadith scholars. He heard from al-Bukhari and others, narrated from 1,500 shaykhs, and al-Bukhari and Muslim narrated from him outside of their Sahih collections, as did others. Al-Khatib described him as being among the prolific, trustworthy, and truthful narrators. The book is not arranged by the names of the Companions, like other Musnads, but rather it is called a Musnad because its hadiths are musnad (have a complete chain of narration), and it is arranged by chapters. It was authenticated by Irshad al-Haqq al-Athari. It contains musnad hadiths, many of which are sound (sahih) or good (hasan), and some are weak (da'if). Its importance is evident from the frequent citations by Ibn Hajar in Fath al-Bari.