On another note, the tricep kickback resembles a single arm triceps press down, the only difference is in the kickback your rear and lat/teres major complex has to be strong enough to keep the shoulder extended to keep the upper arm locked in place...which can be problematic for many people, especially when they start using a lot of weight.
On a side note, the long head of the triceps is the only one that is not fully recruited during pressing movements since it crosses the shoulder joint (its also the largest of the three). IMO the only isolation tricep exercise you need is one where the shoulder is flexed such that the long head is pre-stretched in order to recruit. I.e.: lying triceps extensions with the elbows kept in at shoulder width.