I'd give this CD 3,5 stars (if that option was available). In short, the performances are really good (not great in my view). The works themselves are all brilliant compositions with (perhaps) the exception of Beethoven's octet which falls into the shadow of his brilliant septet which is also included on this set.
Here, the question is not about the performances or the quality of the compositions. The only (but valid) reason to hesitate to buy this set has to do with the sound quality on this set. While the sound quality is not downright poor, it is far from ideal; the strings sound excessively thin and constricted and the accoustics overall are below average. Having said that, the violins never sound scratchy despite this and each group of instruments is easily recognisable (the sound is clear enough). The wind instruments sound more natural than the strings.
Interestingly, the oldest recording of the four recordings on this set offers the best sound quality. It is the recording of the wonderful Octet by Schubert. That one was done in 1968 but the other recordings were done in 1969 (Mendelsohn) and 1970 (the two Beethovens). The Beethoven recordings are the poorest in terms of sound quality.
In the final analysis, one gets what one is paying for here: very satisfactory performances of great works in a clear, albeit not rich, sound. However, in view of the sound quality shortcomings: One does not get anything more than one is paying for!