A note in favor of an excellent set
One of my favorite sets, and one of the really great bargains out there, is Orfeo's collection of Mozart piano sonata's from the Salzburger Festspiele. For forty or so bucks, less if you don't have to order it, you can get Arrau and Gilels in KV 310; Haskil, Gould, and Cherkassky in KV 330; Backhaus in KV 331/2; Gilels again in KV 398; and Curzon in KV 457.
This set, along with the Bayreuther Festspiele official recordings (including the 1956 Knappertsbusch Ring and Lovro von Matačić's splendid 1959 Lohengrin), really makes me like Orfeo. In addition to that, they put out the live Beethoven 6th and 7th by Carlos Kleiber, a wonderful Bruno Walter Beethoven 9th from 1955, Giulini's 1987 Das Lied von der Erde (my personal favorite) and the Schreier/Schiff/Schumann set. They really do a good job, both from an obvious musical standpoint, and a packaging standpoint. I'll say this: I have respect for any label that touches important stuff that the major labels wouldn't even consider putting out in their historical (or, as I like to say, amortized) recording series.
Back to the recording at hand, though. Orfeo has put together a very diverse and intelligent selection of recordings. While, at first, I was skeptical of having so many duplicates, after hearing the various interpretations, I came to appreciate the diversity of the presentation. Hearing Glenn Gould and Clara Haskil both have at KV 330 was an interesting experience. Arrau and Gilels, too, in the KV 310 sonata is revelatory. The choices that various performers make don't always seem that clear or, even, that important unless you put it in context.
Also, two performers outside of a broader context, Wilhelm Backhaus and Sir Clifford Curzon, make a stamp on the set that is wonderful. I am a particular fan of Backhaus (and, for that matter, though in an unrelated matter, Artur Schnabel), and I always enjoy hearing performers in the grand 19th century tradition, especially in such good sound. His KV 331 is a wonderful, all things considered, performance. Indeed, when I heard it, it displaced Idil Biret's 1993 performance (available at her website) as my favorite.
This is a great set, and well worth the money. Compared to some duds with which I have been confronted in the last few months, I can recommend it happily.