if you are standing up and raising the dumbells over your head that brings in a bit more of the long head of the triceps which is a very good thing as far as bodybuilding goes, but maybe not so important if you are just trying to get strong.
Personally I do a lot of triceps work that emphasises the long head because it makes a huge difference to how your arm looks.
The first Mr. Olympia, Larry Scott (relative of yours?
) used this exercise to get "a long head that hangs down like a shark's belly."
But back to the original poster, the power cage/chains thingy might be overkill for him. Close grip bench presses, dips and close grip pushups are alternatives