I know them all decently well. I wouldn't say any of them are necessarily duds. They are all at least adequate, though the standouts are definitely 8, 9, and I think 1 and 3.
I can't say there are any in the cycle I dislike or have major issues with, although Feltz does take some interpretive liberties (he has some tempo or dynamic quirks), and he does take a 12+ minute Adagietto. I don't particularly like the soprano at the end of 4, but she isn't bad. Reminds me of the wobbly English soprano Gielen employed in his studio recording. Though as I sample it right now she has a VERY boyish tone (obviously a good thing for this song). Jeannette Wernecke.
It's all recorded live with applause, and it's "hot." What I mean by "hot" is there may be some slovenliness in the playing. Nothing distracting, but everything also feels very "in the moment," normally a plus in Mahler in general.