Extended diff breathers Vs "Bellows"

[BlakeNZ]

Can anyone tell me the differences/advantages/disadvantages of running rubber Bellows on the diff breathers rather than extending them higher? I've got all the bits to extend my breathers, but have recently come across these bellow things on a couple of 4WD websites.

[shortylux]

With the bellows your diff becomes a sealed system, which has to better (zero chance of contamination is better than a slim chance)
My concern would be are they durable? Do the get torn off or damaged as you winch through bogs etc?

[tycho]

From memory I think I once worked out that a litre of air going from 60 degrees to ten would contract by about 150ml so that is a decent sized bellows. I went with extensions

[BlakeNZ]

thanks for the replies. I doubt the bellows i saw had 150ml capacity.