Particularly, were they as fiercesome as warriors, as effective in combat and as cruel to their captives?
Was his portrayal of historical Comanches such as Buffalo Hump accurate and/or fair?
During the 1800s, the Comanche were probably the most powerful tribe on the North American continent. Their empire stretched across (parts of) the modern states of Texas, New Mexico, Colorado, Oklahoma and Texas. After adopting the horse from the Spanish they became brutal warriors, choosing to fight while on horseback instead of leaping off once they were in combat (many other tribes never achieved this high level of horsemanship). They used the horse to control vast swaths of territory and take thousands of prisoners from neighboring tribes, Americans, Spanish and Mexicans. The Comanche were also known for their brutality. I remember reading one story about how the Comanche tore open their captives stomachs and left them splayed out in the middle of desert to die. Torture played an important role in inter and intra tribal politics as it visibly demonstrated the power of a particular Comanche band (of which their were many in the region, which is now referred to as Comacnheria). They are often regarded as the most vicious and feared Indian tribe. Not all captives were treated cruelty though, women and children were often taken in and became members of the tribe. A white Texas woman, Cybthia Anne Parker, became the mother of Quanah Parker, one of the more powerful Chiefs on Comanche history, after she was captured (and chose to stay).
The Comanche posed a very real threat to the early United States. Kit Carson, the famed trapper turned Army scout turned colonel, nearly became the second Custer at the battle of Adobe Walls if it hadn't been for his lucky retreat.
I am not too familiar with Buffalo Hump or the books you mentioned in your question, but I do know he raised hell after the Texans betrayed him (shooting Comanches under a white flag after staging a 'peace' meeting).
Comanche Empire by Pekka Hamalainen Empire of the Summer Moon by S.C. Gwynne is alright, but his book is more 'pop' history and is all based on Pekka's work, which is considered the most comprehensive to date.
Do yourself a favor and read Empire of the Summer Moon by S.C. Gwynne.
It's an excellent read about the last free days of the Comanche and their move to the reservations under Quana Parker.
Edit: I should add that it is nonfiction.