Dead angle mirror inside or outside?

Hello, where do you stick dead angle mirrors to, inside or outside in the mirror? Are there specific pros or cons? I recently had the unpleasant experience at the motorway driveway in the dark that I almost missed a car right next to me at the shoulder view. There may also have been a role for the factory’s somewhat tinted rear windows. Anyway, I hope that such small glue helpers will bring something.