JT Nebekerwrote a review of Shimano XT RD-M8100 Rear Derailleur on October 8, 2019
Familiarity: I've used it once or twice and have initial impressions
Had my first ride on the new XT 12 speed derailleur and I am drinking the cool-aid!
Here is what I liked:
1. The install was a breeze.
2. The shifting is crisp and quick. Better than X01 I think
3. Reduced chain rattle is noticeable compared to X01
4. Looks pretty cool
Here is what I really liked!
1. Shifting under load capabilities are no joke! I was cranking thru gears and this thing just took it!
2. The decreased tension on the chain when in the 51t really makes pedaling smooth when grinding up some steep stuff.
A couple of things to keep in mind compatibility wise:
This derailleur is built for the 1x12 systems and can take the 51t or the 45t cassette. If you want to run 2x you will need RD-M8120 and that can only take the 45t.