From what very little I do know, Fields does mostly Osprey books. Doesn't necessarily mean anything bad, because Osprey books are written by Real Published Academic Historians, Good Historians with Doctorates who Need Work, and Popular Historians who Might or Might Not Have a Degree in History. Never read any of his stuff myself. It's probably worth a shot. See if you can locate Goldsworthy's biography of Caesar, though, that's pretty good re: Caesar vs. Pompey.