So... I got it on Blu-ray and just finished watching it.
I agree, Truly outstanding.
It should have done better at the box office but I can see why it didn't.
I've never seen the Civil war from this point of view and the story is controversial.
At times I felt very uncomfortable about how they portrayed the Southern Soldiers.
The short documentary that comes on the Blu-ray version is also worth watching.
They spoke with his descendants both white and black of his extended family.
https://en.wikipedia.org/wiki/Newton_Knight