Napolitano's point -- which was reinforced by Justice Thomas in his 2017 concurring opinion in the NLRB case -- is that Section (a)(3) of that statute is unconstitutional. In fact, the idea that Congress can override a Constitutional requirement by allowing "temporary" appointments based on GS pay scales is laughable.
Well, Napalitano must have revised what he said from when I saw him. At that time he said it wasn't legal and specifically referenced this statute. Now having said that, the statute itself may be unconstitutional. That doesn't matter for the issue at hand. The issue is if this apoointment is legal. Under the current US Code it is. If they want to challenge the constitutionality of the law, that is a diffenrent matter and would be moot by the time it reached the court anyway. The provision on this law is that he can only serve by something less than 180 days.