I am following History of the Saracens particularly to cover the topic on Umayyad. I am finding it that Syed Ali has used quite strong words to highlight the acts of most of the Caliphs of Umayyad.

For instance, he writes:

Muawiyah's character and the circumstances which ensured his success are thus summed up by English writer Osborn, whose view, Syed Ameer Ali expresses, on this point at least are free from prejudice. "Astute, unscrupulous, and pitiless, the first Caliph of the Umayyads shrank from no crime necessary to secure his position. Murder was his accustomed mode of removing a formidable opponent ....."

Keeping in view this you think it is alright to follow History of Saracens by Syed Ameer Ali to prepare the notes? Because the other books/authors haven't used strong words despite the obviousness of the events.

Response from specially those who have secured good marks in the subject would be helpful