Pros: Solid Shifting, Light Weight, Does Not care if the chaing is stressed or relaxed
Cons: Wass concerned about the Carbon cage, but it is still holding up GREAT
Recommendation: This set came on my Specialized Stumppy 29er and it has been flawless for well over a year. The shifts are incredibly PRecise, It doesn;t care if you are grinding up a hill or crusing down a flat twisty section, the gears just jump straight to what you call for. I have crashed several times into rocks and stumps etc.. I have bent my Hanger twice, and the derailure is still solid as it was when new. Coupled with the SX-9 shifters this set is great!
Pros: Durability--I put 5 years on this item, including 4 major accidents requiring derailler hanger replacement.
Smooth--shifts like a dream--always.
Worry free--rarely needed adjustment, no matter how badly I abused it.
Cons: I guess I could grouse about price, but this came with the kit I ordered on my bike, so I didn't think about the specific cost of this item.
Recommendation: When I finally beat this one beyond recovery, I wanted to replace it with exactly the same item. But my LBS only had an X9 in stock and, being impatient, I went ahead and got that. After I put a season on the X9, I'll decide if it was worth the downgrade.
Pros: Crisp shifts, great chain control, light weight, durable, easy to adjust compared to Shimano derailleurs.
Cons: Cost as compared to this year's X9.
Recommendation: I have a medium-cage 2006 XO, and this is because I run only two chainrings and an 8spd cassette, and this review is for the '06 XO derailleur.
This piece of componentry is incredibly precise, it does a great job of controlling the chain, keeping it from beating the heck out of my chainstays, and has never needed to be adjusted at the derailleur. A little cable stretch was easily taken up by the barrel adjuster at my shifter pod.
The medium-cage design also keeps it up out of the way of nasty rocks and limbs.
If price is no object, you like knowing when a shift has occurred, and you find yourself snapping off shifts while grinding uphill, this is the derailleur to have.
It's no surprise that Shimano has looked very closely at the XO & X9 design, and nearly copied it for their '07-'08 XTR and XT lines.