The theory is that if you don't have a license to unfold an MQA then it will play as a regular FLAC file, and not as a master 24/96 as example. This unfolding is supposed to restore the compressed (or folded) part of the song to make it better than CD quality (to magically turn it from CD to a master). The controversy is that there is no way to offer higher quality than CD by compressing it without losing data, so it is seen as a sham simply to make money and is not a real thing. I am not here to argue either side (and there IS a bit more to it than that). As to my ears, I don't like them as much as I do DSD files, so I simply stay away from them either way. I don't have anything against them, I just won't pay extra to have them.
But yes, as time goes by the research is starting to show more and more that they are indeed inferior. In the end I don't care too much because if you believe they sound really better than CD quality, then you are happy and content, and that is what we are all here for after all. Hopefully I didn't start up any raging arguments, but I also hope it was somewhat helpful to you?!