I've found they are a great burnout exercise... but totally ineffective for building any sort of mass. If you want something at the end of your workout to really get a great burn and pump in your triceps (well, ADD to your pump) try a limited range kickback.
I basically stay in the fully extended position and lower the db about 6-8" only... and then kick back up and squeeze... doing this at a weight you can handle for around 20reps or so, usually will give you a massive burn in your triceps.
Of course, it can put some strain on your shoulder, but at the lower weight... that strain should be reduced.
I use this exercise with many of my female clients as it gives them a really good burn and helps with definition more than mass building... which is what alot of them are seeking.
C-ditty