The XTR 2x10 drivetrain represents the top end of the mountain bike drivetrain world. It's the pinnacle which all other companies aspire to be more like- lightweight, functional, durable and fully race worthy. There's really nothing much not to like about such a coveted groupset that's run on the world's top end rigs. The rear derailleur in particular is a workhorse of a mechanical system which provides smooth shifting performance into the exact right cassette cog during the most enduring and heinous conditions. Just click and it's there.