Also that Android only gained the ability to enforce iOS-style fine-grained app permissions (prompting on first use for access to camera, location, etc., instead of a blanket grant at install time) one major version ago, which means that many if not most users can't actually get the benefit without buying a newer phone.

I gather there are some questions around the strength of its app sandboxing as well, but I can't speak to that at all. Perhaps someone better informed will do so.