I loved the SRAM XX when it first appeared.
It had that, weird looking, stooping, b-knuckle. The cable route and cable clamp placing would have been a joke, if they hadn't worked so well. It was an essay in forged aluminium, carbon and titanium. But the most exotic material, magnesium, was reserved for the inner parallelogram plate - the most invisible and forgettable component of the whole derailleur (a part that, on lesser models, is often sneakily made of steel).
Its pulley wheels had silky sealed bearings. Its pulley bolts were not only titanium, they were also hollow. It was completely demountable. It was stunningly light. It was hysterically expensive. So expensive that no one had one.
But best of all, every user-adjustable bolt fitted the same size of Torx key - so not only did you require just one tool - but it was a tool that half your friends didn't even have in their tool kit. How cool was that?
This is a medium cage example. It shows in the SRAM parts lists as existing from 2010, but does not appear in the glossy catalogues until the 2012 model year.