I can see the value of practicing without a mirror sometimes. But, I think anyone would be crazy to practice and then perform without doing some sort of mirror work. Of course, you can video yourself and get similar results. However, the mirror gives you instantaneous feedback in the look of where your hands are and what your spectator is perceiving.
My practice breakdown is:
50% normal practice: sitting around, watching tv, waiting around, during transportation (i.e., long airplane, bus, cab rides)
40% Mirror work
10% practicing on family/friends. (if I can get past their trained eyes, then I'm ready for performance).
And another 10% with other magicians. Magic takes 110% effort!
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