The BEST DRIVETRAIN on the market
It is crazy how large this cassete is, it dwarfs the front chain ring, but it is truly machined perfection.
I made the switch to XX1 this year (2013) and I am in love, I have been a long time X.0 user and have always thought the SRAM solution was unbeatable. But getting rid of the front derailleur and having such a wide range of gearing options in just 11 gears is absolute perfection. I can't imagine ever going back to the old system.