I have a Durga with the Novak 6.5 and a slipper (which is only because the 5.5 wasn't in stock and I'm impatient
).
I've driven it a fair bit since I installed it and nothing has gone wrong except breaking some parts in crashes.
However, I've only driven on concrete and occasionally gravel. I suspect that running in grass or anything with massively varied grip would put a whole lot more wear on the diff.
I really do need to upgrade to the 501 rear diff before I actually melt it.