I think the low shin kick to the legs, along with foot sweeps, are among the things most people simply do not know how to deal with, or process when it happens to them in a self defense environment. They are also high percentage techniques, with low risk to the kicker/sweeper.

Though I generally do not teach these specific techniques in personal protection, as in my experience they take some timing and skill, with that skill (readily developed arts that train them under true dynamics such as Kyokushin and judo) these are among the best self defensive options out there.