FS is a bit of a faff as you still need a mech of sorts to tension it unless its a concentric BB like a DMR Bolt or Kona-A.
The rolhoff and alfine ones get mentioned a lot.
I’d add a lower chain guide like a blackspire stinger to take out the slack when the bikes at rest (most bikes get longer chainstays at full compression and a lower chain guide will have less effect at that point).
Before you ride it, take the shock out and check the chain tension at all points in the travel, put it in a bike stand and loop a zip tie through the shock mounts so you can pull the wheel up a bit at a time to check. The chain needs to wobble like there’s some play on it, but not be loose, and definitely not tight enough to ‘twang’ like a guitar string at any point!