Review on Top-Notch Performance: SHIMANO Ultegra Di2 R8050 Short-Cage Rear Derailleur Unleashed! by Eric Hanson

Excellent switch for Di2. I switched from a short Ultegra derailleur that only allowed a maximum cassette size of 28T, which sucks in the mountains. This allowed me to upgrade to a 34t cassette for specialty mountaineering. I've heard you can go up to 36t, but Shimano don't make 36t road cassettes. The switch works well and shifts smoothly. The action is light and crisp, firing perfectly every time you press the button. No more cutting or further pushing the lever to get the gear you want. You can use the Shimano app to update the firmware and then control the shifting. It's really customizable.