In the process of switching several of my bikes over to 11-34 cassette compatible which requires the RD-R8000 mid-cage derailleur. Have ridden Shimano Dura-Ace and Ultegra lines for years. Ultegra delivers excellent quality and performance at a more affordable price. Definitely recommend this derailleur if you want to be able to accommodate up to 34 tooth cassette.
This derailleur allowed me to upgrade my cassette to an 11-30 cassette and its just been great. The shifting is quick and smooth and it just looks great too. The trickle down technology from the Dura Ace, makes this decision a no brainer.
I bought this derailleur for my 1X cross bike. It worked flawless with a narrow wide chainring, 11-30 cassette and a chain catcher for a full season of cyclocross. Comparing it to my XTR 9000 derailleur, its basicslly the same design without the clutch. The short cage is longer than the previous version so it has more Tooth capacity. The B knuckle on the Ultegra is the exact same size as the current XTXTR so you can use the WolfTooth Goat link perfectly and run up to an 11-40 cassette with no issues. The chain tension spring is stronger than the previous generation derailleur and there are two tension settings. It comes stock in the lighter setting. Because it uses the Shadow design, the derailleur doesnt stick out as much as the older design so its more protected in the event of a crash.