Amadeus Quartet was very highly regarded in its heyday, and was generally considered to be one of the world's leading quartets. These recordings were made in the 1960's and 1970's, and the sound is consistently very good. The group plays with great vigour and energy, but also with finesse and attention to detail, as is fitting to a group of their caliber. To me these recordings sound very Mozartean; this is classic Mozart playing at its best.
In fact, I prefer this kind of "old-fashioned" sound far better than modern "improvements" such as SACD, DSD, DXD, or whatever, as they often sound much better in normal two-channel stereo. Maybe this has something to do with the fact that my stereo system is rather old (from the mid and late 80's, that is), and I have often found it to be the case that a well-engineered older recording just sounds better to my ears than any of the more recent state-of-the art innovations. Old goes well with the old, maybe... This may be just a matter of taste, however. (Boy, did they make good stereo systems way back then - not a trace of planned obsolescence...)
The booklet has detailed information about the recording times and venues, although it does not say if the original recordings were remastered. But that does not really matter, because, as I said, the sound is just fine. There is also an informative essay on the quartets by Tully Potter.
The only real drawback seems to be that the Amadeus Quartet apparently does not play all of the repeats, so some movements are shorter than with ensembles who meticulously observe the repeats. I don't mind that very much; if fact, this approach seems to make the quartets themselves more concise: more playing, less wallowing.
As a bonus, this set also includes excellent and spirited performances of three of Mozart's best-known divertimentos, K. 136-138.
So if you are a seasoned collector or just want a good overview of the Mozart quartets, this set is a worthy addition to your library. Even if you would later decide to buy more interpretations of these works, this set is a great point of comparison from a purely historical point of view, and as a document how Mozart was interpreted by one of the great quartets of the last century.