When it comes to effectively conducting the chorus of your cassette, few options can rival Campagnolo's Chorus 11 Rear Derailleur. The Chorus model does make some concessions to its more expensive Record and Super Record counterparts. Namely, it makes 13 and 17 concessions, respectively, which are the number of grams of extra weight it carries in comparison. As far as function goes, the Chorus has the same internals and receives the same updated operation, but at a price point that appeals to the self-sponsored cyclist.
The brains of the derailleur are the cross section springs, which have rectangular cross sections for an increased return load. In conjunction with the new Chorus shifters' cable pull ratio, this translates to faster, more precise shifting — in both directions.
The parallelogram's motion as you shift across the cassette has also been revamped for 2015. It corresponds to the size of each cog, so the top pulley stays the same distance away from the cassette whether you're using the crit-spec'd 11-23 or the all-terrain 11-29 cassette. This keeps the chain seated securely on the cassette at an angle of engagement that transfers maximum power into propelling the bike forward. It also reduces wear on your chain and cassette.
The parallelogram and cage are made with carbon, while the upper and lower bodies are made from a technopolymer that's lighter than metal but can still stand up to any abuse from the elements or the occasional user error (read: crash). The Chorus model's pulleys don't get the same lightweight polymer of the Record and Super Record derailleurs, and its parallelogram doesn't have the weight-reducing cutouts. It also uses steel bearings and small parts instead of the ceramic bearings and titanium of its more expensive counterparts.
The Campagnolo Chorus 11 Rear Derailleur is only compatible with 2015 Campagnolo Super Record, Record, and Chorus drivetrain components. Compatibility can be confirmed by matching the letter on the body's underside with the corresponding markings on your other drivetrain components.