Ops Manager UI (4.0 -4.4) does not allow downgrading of Feature Compatibility Version (FCV), once the FVC has been upgraded to a higher version. Ops Manager automatically
removes the lower version from the supported FCVs once upgrade completes. But the cluster deployment allows downgrading one level using shell commands. This limitation makes it difficult when planning an upgrade as regression process are more difficult.
We are in the process of upgrading the environment from 4.0 to 4.4 (which requires an intermediate upgrade to 4.2.). So the downgrade process is so difficult with Ops Manager UI.