I have mixed feelings about Schwarzkopf -- her early 1950's Strauss songs and Mozart opera recordings are lovely, while the later remakes show her working rather too hard to make the requisite effects, and she can sound mannered at such times. In operetta, however, she's very appealing (I very much like her early "Merry Widow"), and in this 1957 recital she sounds totally at home with both the dialect and the style, and she shows too how to characterize the songs according to the character and to the dramatic situation. The arias from "Der Graf von Luxemburg" clearly distinguish Angele Didier's moods, and the different singers of the "Vogelhaendler" arias are likewise made distinct and brought to life -- "Christel von der Post" is an absolute charmer. And I would bet that you couldn't hear "Meine Lippen sie kussen so heiss" done more insinuatingly and seductively. The loveliest, perhaps, is the simple song from "Boccaccio," made more effective by coming after the self-advertising high spirits of "Was ich in Leben beginne" from Millocker's "Dubarry." Schwarzkopf knows this is "pop" music of its time, and she can put it over.
The sound is OK for 1957 -- the voice is perhaps a bit closer to the microphones than in the contemporary opera recordings, and perhaps as a result it can seem a little glassy at the the top. At times too you're aware of Schwarzkopf positioning her voice for a high note at the expense of some of the vowels -- but these are not major concerns. This is a winner.
NOTE: I am concerned, though, by the high price in the UK! You can get it in the US for less than half this price -- and for five bucks, used.