Obviously, he's not a historian so much as a commentator that includes a lot of history in his commentary. I'm not an expert in most of the history he talks about, but his sourcing (Family Properties, The Warmth of Other Suns, Race and Reunion etc.) seems good.
I just bought his new book and am looking forward to reading, so I wanted to know of there were any red flags in his interpretation of the scholarship he's dealing with.
His history's generally pretty good. Those are reputable sources. He's heavily influenced by the new wave in southern historiography, which tends to rile those who are operating under older assumptions. The big shift in the last fifteen years has been from viewing slavery as a dying backward relic to the cornerstone of southern society and the economy, a system which achieved efficiency through the application of "calibrated pain," to quote Ed Baptist, and certainly in no danger of imminent demise in 1860. His rhetoric can get a bit strident at times, and sometimes I think he slips over the edge into polemic, but I am a southern white guy, so that may be a touch of my own bias creeping in. I'm sure it's much more difficult for him to treat this subject dispassionately, as someone descended from the victims, than it is for me, as someone whose ancestors perpetrated the institution.