I also strongly believe a rear mirror is a very good asset, not only to watch what's going around the tail rotor, or on a underslung hook but also to help in decision taking when dealing with badly locked cowlings, smokes, sudden increase in vibrations, change in noise.... I remember having used a small rear mirror fixed on a broom stick just to look if the loads carried in side external baskets stayed in place....Of course the rear view bullet camera is a smarter solution as long as the vibrations on the tail section don't affect the visual and that the lens can be kept clean.