I've always found decline skullcrushers to give a good burn in the tri's I never got with other lifts though, just have never tried them with dumbells.
Agreed. We get a lot of tricep stimulation from various heavy pressing movements. A few isolotion movements just help to stimulate a few more fibers in the tri's. It is usually best to pick one or two and stick with them so that you can make continual progress on the weight handled on the movement. Adding something like this movement can be nice for short periods of time to help get out of a training rut or just for some nice diversity.