Sometimes little things go wrong. Take Brian's Surly. Somehow he managed to strip a rather important bolt on his rear derailleur which sadly necessitated replacing the whole thing.
While it's never a good feeling to have to replace a bike part before the normal end of its service life, sometimes it can be an opportunity to make improvement. Brian decided to to do just that. Rather than just putting another Sram Apex rear derailleur on his bike he decided to upgrade to a Sram GX derailleur instead.
Technically the GX parts are from Sram's mountain bike specific line but lucky for Brian, Sram mountain and road 10 speed derailleurs are interchangeable. For a bike that sees some off road use the Type 2 clutch mechanism that the GX derailleur uses is a benefit regardless of what kind of bars your bike has. You see the Type 2 design keeps the chain from bouncing around so much when the going gets rough. That means less chances of dropped chains, better shifting and less noise. All things that any cross terrain bike will benefit from.
Good call Brian. Ride on.