1. The Union tool
When switching to Manual method and then adding fields up stream, the result is a warning "Field was not found". I don't look for warnings. This should create a red error. Having fields fall off the workflow is a pain.
2. Unique tool
Changing fields upstream causes the tool to error out when the workflow runs. No issues are shown before the run.
3. Having containers all open up when I reopen a workflow is a nightmare when you have 20+ containers all over lapping.