Hmmmm. Personally, if the law was unconstitutional, I'd rather not have that on my record.
Better the judge dismisses the charges than to have my personal record say that I was arrested on a felony, jailed, tried and found not guilty.
But you're saying the Supreme Court suggested a trial and acquittal, huh?
The District Court dismissal was a rejection of the prosecution's attempt to hold a trial. The Supreme Court reversed that dismissal, over-ruling the District Court judge. Barring any other impediment to a trial, then the prosecution would get its way.
The Supreme Court indicated that they lacked "judicial notice" that the weapon in question was useful to a militia. That is equivalent to saying, "the District Court must determine whether a short-barreled shotgun is useful to a militia in order to determine whether the possesson of THAT WEAPON by MILLER AND LAYTON is protected by the Second Amendment". Such a finding of fact is subject to dispute by the contending parties in a trial, evidence is entered by both parties, and the jury will be charged to decide what the facts of the specific case are.
The District Court judge would be obligated to explain "the law" to the jury, detailing which facts would have to be true in order to decide guilt. The law in this instance would include NFA 34, the Second Amendment, and the Supreme Court's Miller decision. The judge would probably NOT explain to the jury what the basis of each law is, but rather would supply the legal ramifications of taking into account all three sources of relevant law. The jury, for example, would be unaware of the Supreme Court case. Knowing whether the Supreme Court was unanimous or not would be prejudicial, since the Court vote wouldn't change what the law is.