Perry Hallwrote a review of SRAM X9 Type 2.1 Rear Derailleur on August 4, 2015
Familiarity: I've used it several times
Don't drop that chain with the type 2.1 rear derailleur. Great quality, great shifting performance, and the new type 2 is fantastic and keeps the bike quiet. I have these on a few bikes and would purchase again!