Swapped my trusty X0 out for a FR Zee rear mech. Feels strange going from such an expensive mech to such an affordable one but man it works.
I like quiet bikes, my Brooklyn DH sled is one of the quietest out there and my HD had got pretty quiet too.
So I kept my XTR 970 cranks with 9 speed 22/32 rings and a bash and changed to KMC 10speed chain. XTR rear shifter an XT 12-36 cassette and the wider range (12-36) rear mech.
Very nice, very quiet, clutch improve that, tucked out of the way and improved my low range (we have a lot of steep climbing where I am)

A very satisfying and inexpensive "upgrade" from X0 lol
Ironically as everyone seems to be shifting to SRAM and XX1 I seem to be going to Shimano for the first time in 10 years.

Anyway, this is a good little mech, a baby Saint, and a breeze to setup