This issue of the 1941 "Heldenleben" is far superior in sound to the Teldec issue, which is overly filtered and muddy in sound. Still, there is some harshness and stridency here, as in a number of Naxos historical issues; I would love to hear a Pearl or Tahra transfer of this material.
I used to favor the Philharmonic performance from 1928 (superbly transferred by pearl). Now, after hearing this generally good issue, I'm not so sure. It seems as though Mengelberg had become more thoughtful and reflective in this latter performance, eschewing virtuosity in favor of lyricism and poetry. The final section is especially moving in the 1941 performance, and the playing of the Concertgebouw is more subtle and refined than that of the Philharmonic. Personally, I wouldn't want to be without either of the Mengelberg recordings.
"Tod und Verklaerung" is a completely different story. I first heard this performance over FM back in 1961, from terribly worn 78's. That hearing did not prepare me for this harrowing account of the score. From the opening drum beats, the grim power of this work is faithfully reproduced by Mengelberg, and the concluding transfiguration music is blinding in its intensity and nobility. I have never heard a performance in this class before, and I nominate it as the essential "Tod und Verklaerung." Who needs Szell when you've got Mengelberg?