I had a Kieffer one and it cost me about £18 and was fantastic, passed it to a friend as it doesn't fit my horse, siliar effect to aurigan and lasts well, hope that helps.
MMMmm not sure, would be surprised at Keiffer making bits out of nickel and mine was very hard wearing, my old horse wore it everyday for over a year and it's still going strong on my friends bridle. It looks like a normal stainless steel bit in colour. I think Shires do some german silver bits if you look at their site is may say more?
I find them better in terms of mouthing properties as the aurigan, or 'German gold' tarnishges easily and then looses its mouthing quality.
i use mostly the silver and all of mine are KK bits. It is similar to the Kangaroo bits that were made a few years ago and was known for its quality.
Neue Schule also make bits out of this alloy.
I think you can see that these are all quality and are used by many riders like me.