Alfred Einstein oversaw K3, which was the first radical overhaul of Köchel. He was a scholar who was deeply grounded in Nineteenth Century German Humanism. This book is the product of his lifelong interest in Mozart. Purchasing it does not entail a visit to the Valley of the Dry Bones where only desiccated scholars draw sustenance; it was written for the Common Man or Woman.
Part of this book is antiquated. Recent scholarship has completely overhauled our understanding of Mozart's creative process. Similarly, the chronology of many works as advanced by K3 has been revised, not least by Alan Tyson Mozart: Studies of the Autograph Scores. If you purchase Einstein's book, be mindful that Chapter 8 'Fragments and the Process of Creation' is thoroughly outdated.
There is a difference between truth and fact. We can still profit from Einstein's knowledge and his deep love of Mozart. There is no better depiction of Mozart as an Eighteenth Century composer, a man among men. Words often falter when applied to music. Thankfully Einstein is the master of the analogy; what else can one use to encompass such a demi-god? Mozart's organic growth as a composer is well traced. Again and again, he imparts illumination.
There are sunspots: Einstein underrates the E Flat Major Concerto - K 482, the Queen of the Realm; he famously neglected to include the Haffner Serenade; he also stands staunchly in the anti-Constanze camp (the poor woman was incessantly pregnant during the eight year marriage); his review of the Clarinet Quintet - one of the wonders of the world - is somewhat underwhelming. Nor am I convinced that Mozart should be labelled the "most Catholic of composers" - to wit, his espousal of Freemasonry (and a certain guy called Anton Bruckner has stronger claims).
Even so, every page will deepen your understanding "of the miracle that God allowed to be born in Salzburg." [Leopold Mozart] This book is a classic. Come Judgement Day, it will still be in print.