I used to feed Darwin's.
It was an OK food, certainly better than kibble, but it is 30% veg.
That meant my GSD had to eat a lot of it to get what he needed, and it still was not enough. He was eating 3 to 4 pounds a day and he was too thin.
Also, it contained a lot of sweet potato and beets, which had lots of sugar. His poops were inconsistent, many times too soft.
I switched to My Pet Carnivore and never looked back. He has never looked better, nor had better stools, in his life.
Reelraw is good, too, and they ship free if you order in 50 lb increments.