To add to the 11 speed shimano working thing. It isn't a specific 11 speed shimano RD that has the same pull ratio. That specific 11 speed RD is made to work with up to 51 tooth cassettes while the others are rated for 42 or 46. I just bought one myself but I also bought a 11-51 cassette, keeping my hard tail 11 speed but still need them easier gears.