They way I see it is this: if pressing a button of your choice is not an expression of free-will, then nothing is, because otherwise you can just say that free-will determines whatever in the brain is determined by quantum noise, so that it becomes an empty concept.
That said, it's true that we don't know very much about the inner working of the brain, but I believe that we know enough to say that it doesn't store and uses quantum bits for elaboration.
But even before invoking that, Lisbet-like experiments directly link free-will with available neuronal data: I'm not saying that it's a direct refutation, but it's a possible direct refutation.
My pet-peeves is the author not acknowledging the conclusion, instead saying that the experiments were not impressive enough to constitute a refutation of his claim.