"Second to shifting, chain management is the most important job a rear derailleur has to perform. Today’s ultra-light long-travel trail bikes have us riding rougher trails, faster – all factors which collude to pop chains off both the cassette and chainrings. Enter Shimano’s new Shadow Plus design, which allows the sprung lower pulley cage to be ‘locked out’ below its parallelogram linkage, dramatically reducing chain movement." - Bike Radar
This little gold anodized lever is what all the fuss is about. It is supposed to keep the derailleur cage from losing tension on rough trail and letting your chain beat everything within reach of it. You know, it's that clanking and beating sound that beats and scrapes your chain stay to death unless you have one of those cover/ protectors on it but it's still noisy metal clanking sound in rough terrain.
We loaded up and rode Warriors. Oh yea, rocks, roots, rough, bumpy Tennessee single track for this test! It was quiet muddy as you can tell below. Melissa went along with her Haro, she's already progressed enough and is wanting a carbon mtb! Is the TBRA Tennessee State Road Race Champion coming to the dark side??
When we got there there was trash all over the parking lot.... lazy pricks! There's a trash can 20ft away! Jeeezz!!! I quickly put this trash in it's place before we rode. #*^&%##$%&^& !!
Ok.... the test. Once on the trail I started easy to make sure Melissa was getting used to Warriors ok, it was her first visit there on a mountain bike. After I got into the rocks and rooty sections I let the BMC TE29 roll.... wow! Silence! Pure silence! No clanking, banging chain noises what so ever! Holy cow, IT WORKS! The shifting?? I noticed just a little drag maybe but to tell ya the truth if I hadn't been biased by the review online I don't think I would have even noticed it it's that minuscule! So it was "hardly an issue". It shifts as easy, if not easier, than my DynaSys XT that I had on the bike before this test if that says anything... I'm not running my normal housing all the way back on the 29 right now either so I may not be able to tell anything at all after I re-cable it later. On a carbon bike I think it would even be quieter! Yes I do! It really lets you hear things better without all the clanking you normally get in the rough stuff. I'm impressed!
So if someone doesn't use this derailleur for the excuse of "increased drag" in shifting. You're an idiot... plain and simple or you're P/O.... or a SRAM fan.
So in closing I would whole heartedly recommend this part for your bike and I give it an honest 4.5 "scoobs". The ONLY reason it didn't get a 5 star (scoob) rating is this technology ONLY comes on the XTR (right now) and it's pricey! $249.99 retail, ouch! I bet the XT has this by next year... IT SHOULD! All you die hard 9 speeders..... sorry!!! If you ride a mountain bike... YOU WANT THIS, it's that good! REALLY!