The Gielen set is uniformly excellent performance and soundwise.
In addition to the above boxed sets, and after reading your post, I took a head-count of the rest of my incomplete Mahler sets on CDs.
Total of 126, by many different conductors and on many different labels.
I had some of Neumann's on LP but sold ages ago and never replaced.
I do admit to having even more complete sets of the Beethoven symphonies.
It’s an affliction I suffer from.
My first Mahler LP exposure 1970, The picture caught my attention, was able to get a Japanese reissue on CD. Ormandy and Phila. O.