Mozart wrote only two piano quartets in 1785 and 1786, either side of a nice little opera called "The Marriage of Figaro". So these are mature works; unfortunately they did not meet with approval from the Viennese beau monde of the day, apparently being too "serious" for their fragile taste; Mozart voluntarily withdrew from the publishing contract for the first yet still had sufficient faith in a combination of instruments and musical form which he virtually invented, to compose a second one. The accusation of "heaviness" seems absurd to modern ears - as it probably did even to some of Mozart's more discerning contemporaries; there is plenty of insouciant playfulness, as ever masking underlying shadows.
The stand-out for me in this highly recommendable budget recording from 1984 is the pianism of Deszö Ránki: fleet and fluent in his rippling runs, highly sensitive in his use of dynamics. The merits of his Hungarian compatriots, three members of the Eder Quartet, are well known; they combine beautifully and respond to Ránki's lead in eschewing grandstanding in favour of delicacy. In both works the central movement - an andante and a larghetto respectively - forms the emotional heart of the piece, the strings singing while the piano embroiders elegantly or comments wistfully. This is not Mozart's greatest, most profound music by any means, but it offers many delights to the careful listener - and this Apex reissue offers a very economical means of getting to know the music played by consummate professionals.
My subsequent reduction of one star results from a fair observation by a fellow reviewer that the sound is lacking: it's a bit muddy below and thin, even screechy, up top. This doesn't compromise my listening pleasure as it might for others but it's only fair to remark on it. I try not to be a "reviewer" in inverted commas.