Vinny Maurowrote a review of Shimano XTR RD-M9000 Rear Derailleur on June 23, 2017
Familiarity: I've put it through the wringer
XTR stuff is obviously great. Whether you prefer it over the SRAM offerings is purely personal preference really, I've had both recently and couldn't even say which one I prefer so I just go for whatever I can find the best deal on. I've had this derailleur for a few months now and it has performed flawlessly. My only beef, and the on area where I think SRAM is the clear winner, is in how you disengage the derailleur to remove your rear wheel. On SRAM there's a handy lock button, so you just extend it full and lock it in that position and it stays out of your way. Instead of that option, Shimano just let's you flip a lever to disengage the clutch so that there' s no resistance. This means you still have to flip the derailleur while pulling the wheel out (I know, life is SO HARD), but more importantly it means you have to remember to re-engage your clutch once your bike is back together. I always forget until I'm part way into my next ride and wonder what all the noise is about.
That's a pretty minor, possibly even stupid, complaint so I still give it 5 stars. If you're shopping for this stuff you're probably making lots of decisions about where to splurge for XTR and where to save some pennies (lots of pennies) and go XT. Both are great really... I've always done as much XTR as the pocketbook allows to save weight, but I've also always been happy with both groups.