According to Wikipedia the two opus 3 SQs included in the set are commonly regarded as spurious Haydn, authentic Hoffstetter.
FWIW, comments qtd from another forum:
Received this yesterday, and while not the greatest Haydn performances, the sound is hardly an issue. Better than many 1950s recordings, ex. the Hungarian Quartet set of 1953 for which Art & Son was getting blamed for the horrible sound, while I suspect they did the best with a bad lot without drastically changing the sound. They did the work here, and so far, superb. And a bargain! Now, if Warner would set them on the Lener legacy, but then I would be dreaming.
Despite their age, the recordings seem good enough, if not up to the sonic splendor of the Angeles Quartet's recordings of the complete quartets (Philips 464 650-2). The older Pro Arte recordings did not contain the complete Haydn quartets, but there were a great many of them nonetheless. This earlier set contained three of the quartets of "Op. 3". As B. H. Haggin noted at the time (the 1930s), the performances by the Pro Arte tend to be mediocre.The Angeles Quartet set, noted above, is the best choice for present-day recordings.
. . . the price of the new Warner issue is right and the recordings are a cornerstone of any Haydn collection.