I mix a lot of Trance so I need to use key numbers. However, I use the Camelot numbers in every possible way - I'll follow circle of fifths or move a full tone or a semi-tone or to a relative major of the next minor along...
And sometimes I just wait till a really chunky beat or break and then loop it and jump to another track.
I also find that many of the errors of mixed in key are just semantics - they'll get a tonal centre but it might not be the dominant one in the song.
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