I've never used a goosneck before, never felt the need to buy one.
Only time they might be handy is conny roofs but I've managed thus far without one.
they are so much lighter than the plastic goosenecks....i have 3 or 4.....maybe 5..... 
Only 50g lighter than a plastic one
But they are not adjustable angle are they ?
I ended up using an old slx section to fix my extreme pole so it's already heavier than standard now anyway.
how many times do you adjust your plastic gooseneck during your normal working day?i bet hardly ever.....
Quite a lot
If cleaning top windows over a conny tend to need to straighten the angle, if doing velux needs to be more 90 degrees
If im working in a tight space, again needs changing.
i change it a fair bit, its only 2 seconds i do it without thinking really but a fixed angle would make it awkward.
another couple of years of wfp cleaning and you wont bother.....
When i order a new pole I will try a carbon gooseneck.
I've tried rinse bars, swivels and found them no easier and I can't imagine a gooseneck changing my life but I'm willing to give it a go.