I just want to endorse what other reviewers have said. This is an absolutely astonishing bargain. Three of the operas were recorded in Vienna, more than any other the city of Mozart, even if it didn't always appreciate him as it should have done in his life, with the Vienna Phil. and with the foremost stars of their time - della Casa, Christa Ludwig, Dermota, Erich Kunz, Cesare Siepi, Gueden, Danco, Corena, Walter Berry and others, with Krips, Bohm and Erich Kleiber directed, and the fourth - 'Die Zauberflote' - is a famous Berlin recording with Streich, Greindl, Haefliger, Maria Stader, Fischer-Dieskau and the wonderful Ferenc Fricsay conducting. There are some glorious voices and wonderful performances here, and it's nice to hear singers like Fischer-Dieskau and Berry, for example, fresh-voiced and early in their career. The recordings, from 1954 and 1955, are very good for their time, well balanced and faithful to the voices. In sum - very distinguished accounts in faithful sound, and for no more than pennies. I see no reason to hesitate!
While none of these four performances might necessarily be a first choice for an individual recording, as a super-bargain box set this is self-recommending, featuring as it does an array of the finest German singers to be found in the mid 1950's conducted by four master-Mozartian conductors in Böhm, Kleiber, Krips and Fricsay respectively. The sound is remarkably clear early stereo and the packaging attractive, being the by now conventional format of a sturdy box containing cardboard slipcases. The only obstacle to acquiring this as, or for, a Mozart novice, is the lack of libretto or even synopses; it is obviously assumed that the collector already has them, so if you do decide to give this to a Mozart tyro, remedy the omission. At this price - even cheaper on Marketplace - it is absurd to complain but remember that "Così" in particular suffers from cuts.
It is true that some individual performances are less than ideal; Poell's Count Almaviva is blustery and dry of voice, his Italian intermittently Teutonic - a flaw occasionally apparent in other singers, too; in "Die Zauberflöte" Greindl's Sarastro is a little lugubrious and Stader not ideally pure as Pamina but you do get dialogue unlike some contemporaneous versions and there is a sense of ensemble about each opera rather than that impression some more modern recordings give of a random gathering of star singers. But talking of stars, just look at some of the names here: Lisa della Casa, Christa Ludwig, Cesare Siepi, Hilde Gueden, Rita Streich, Suzanne Danco, Anton Dermota; so many great singers sounding as fresh as you could wish. (Here, to select an example at random, Dermota shows off his breath control by delivering the long phrase of "cercate" in "Il mio tesoro" in one breath unlike in other recordings.) The quality of performance, interpretation and sound is high throughout all four operas and this set represents a supreme bargain.