You can run different Replicator editions in your replication network. For example, in a hub and spoke topology, the hub can run Replicator Enterprise or Standard edition for immediate and multi-threaded replication. The spokes, with less traffic and changes, can run Express edition.
Look and Feel Replication is only possible when both the source and target can process look and feel events. For example, you cannot replicate look and feel changes from a Standard edition source to a Express edition target.
Workflow associations and instances can be applied to targets running Express edition, however the Express edition farm cannot replicate these actions back to an Enterprise edition farm. If the workflow is processed through replicated SharePoint objects, for example, tasks in an Approval workflow, then you can successfully process a workflow on the Express edition farm.
Alerts can be replicated from Standard edition farms to Express edition farms. Changes to alerts are not replicated if they occur on a farm with Replicator Express edition.