Derailer - Rear - Shimano Deore model M592, Shadow
The current top-of-the-line 9 speed rear derailleur made by Shimano.
Shadow is Shimano-talk for a rear derailer whose body doesn't stick out as far, and is therefore theoretically less likely to run into a rock. It was probably an overreaction to an incident like that, and in a rare circumstance it has to work, but for it to "work" you'd have to pass the rock with your body and legs, and then turn a corner just the wrong way and hit a rock.
The "shadow" rear derailers don't have barrel adjusters. That's a bigger deficit than the "shadow" part is a benefit, but as long as you have a RapidFire shifter with a barrel adjuster, that's not big deal.
For wide range gearing—like for touring or trail riding.
This is a good old rear derailleur that'll never let you down. The Deore was introduced in about 1985, and there have been probably 15 variants, all "Deore" since then. It's Shimano's M.O. All of them have worked well, no surprise, since the Deore is a Shimano derailer after all, and it is in the upper chambers of the derailer line, and is arguably -- and we'd argue it --- the best value.
Shifts to 36t. An excellent choice, always. Nobody, but nobody, ever squawks about a Deore.
Shimano code name RD M592 SGS
MADE IN JAPAN
---------Feb 13, 2020 NOTE:
These 9 speed Shadow Deores will soon to be out of production, supposedly sometime this year, so stock up if you like it lots. The Shimano replacement for this won't be 9s.