I disagree with your statement that a controlled round unit cannot double feed. I stated previously that the extractor does not fully engage the cartridge until the round is well into the chamber. If you short stroke before engagement you will have a double round jam. Even with the finest Mauser made. I have played with enough of these to know that doubles can happen with any action. Until there is significant (not full) engagement of the extractor, the controlled round feed doesn't do anything that a pushfeed doesn't do.

I like controlled round feeders, don't get me wrong. I like pushfeeds that work as well.