Problems with Mixed in Key, itunes playlists, Traktor & Serato

Where did you save the key to? If you saved it only to the “key” mp3 tag, then iTunes cannot display that.
I always save it to comments, then you need to refresh the iTunes tag to show that (mixed in key in the last “help tab” does tell you how to connect iTunes correctly to refresh tags).
So actually: Read the mixed in key manual carefully and it will work out.