Both of my cameras are impressive, and work very well. I've decided to spent more time with them and learn a lot about the feature options before using them for work. I'm using other cameras for the time being for assignments.
When the 1-DMKlV came out, a lot of people had issues until they learned more about the complex AF.
A friend of mine, an experienced AP photo bureau photo chief in a big city, had issues with his Mark lV until he learned the optimal setup for AF. His results then became consistently excellent.
Rudy Winston, a good guy and tech expert from Canon, has an online series describing the new 5D / 1DX AF system.