There are very steep legal penalties for lying about it, and it’s not available in China, so on balance I think it’s a reasonable risk, especially since Android makes no such promises.
That being said, I can use open-source projects like Syncthing or Owncloud to handle my syncing, and skip the whole mutual trust part. Though I'm sure the NSA does a wonderful job auditing Apple's private codebase, for whatever sense of security that offers.