The Intro starts on page 17. There is no TL;DR version of this Brief, it's already as short as the authors could make it.
Good stuff on page 43 onward, digging into historical tradition vs the current application of "dangerous and unusual". It seems that back in the old days, the test was applied on a case-by-case basis depending on the weapon used, how it was used, and the actual nature of the crime. It was up to the JURORS to decide if it was dangerous/unusual.
Compare that to today's pre-compiled "naughty lists" that allow convictions without the defendant having a chance to challenge the dangerous/unusual accusation. Today, the judge will just instruct the jury as to whether a weapon is dangerous or not and the jury won't put up a fight, they'll just side with the government without ever hearing testimony about the true nature of the weapon and why the prosecution/defense disagree that the weapon is not particularly unusual or dangerous.
Hopefully SCOTUS agrees that it's time to get back to basics. The "feature bans" and restrictions are hopefully on their way into the dark corners of history and remembered as gross authoritarianism. The ATF vertical foregrip rule and the California "featureless" pistol grip (which features a huge shark fin) rule are perfect examples of such authoritarianism... dictating right down to how you can and cannot HOLD the gun in your own hands.