Only on the market since 2012, the vibration-damped rear derailleurs (Sram Type 2 or Shimano Shadow Plus) are an innovation with real benefits. They reduce chain slap and improve chain guidance. They are now available for all relevant groupsets, from Deore to XTR and from X7 to XX1. That's why it's worth looking out for them when buying a new one or, in the case of a replacement, it's better to get one straight away. A few extra grams of weight and the slightly higher price are not that big a deal. The differences that determine the price of rear derailleurs are rather the choice of material, processing quality and bearings. This makes it possible to achieve even smaller improvements in shifting forces and precision and reduce weight. In general, modern rear derailleurs work at a very high level.
Conclusion on Shimano and Sram derailleurs
In purely functional terms, you don't need an XX or XTR rear derailleur. Bike companies often conceal compromises in the drivetrain with an expensive rear derailleur. Better to choose higher quality shifters! The vibration-damped chain changers (Sram Type 2 or Shimano Shadow Plus), on the other hand, are a real benefit/added value.
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