The cover picture gives a reliable clue to the performances here: youthful and unpretentious.
I remember listening to the BBC "Building A Library" for the Debussy sonata, being slightly over-awed by the magnificence of the playing by the Grand Masters; then the van Keulen and Brautigam was reviewed briefly as an 'alternative and youthful' performance and I knew this was exactly what I had been waiting for.
By way of a comparison the first movement of the Debussy, by Yehudi Menuhin and Jacques Février
I am reminded by this of a review by the music critic Raymond Tuttle of an unrelated piece, where he wrote
"Gieseking achieved a paradox with these recordings: he devoted so much care to them that they seem absolutely artless. The pianist who mastered Beethoven's epic edifices also had the modesty to efface himself in front of (these) innocent creations. Not once does he say, "Look at me!" or "Now I'm going to show you how beautiful this is." He simply plays the music without condescension or apology"
I've never understood why Ronald Brautigam subsequently devoted himself exclusively to the fortepiano and the Romantic period