NetMulticast will cost more than a standard replication. The RPC system cost more than replication. I can’t give you detail on this, but this have be mentionned many times on network thread in the forums.
What were the pro to use NetMulticast instead of a std replication?
If you are looking for instant replication, you can tell you actor to replicate immediatly and not wait until the next replication time.
As far as I know, NetMulticast has no scope. It will call the client function on all connected client. So there are no “bandwith” saving and it may be the opposite if you set it as reliable.
ShooterGame approach is what’s Epic is using in UT4 also. It’s was also the same approach in UDK, UE3. I think you can rely on this design to setup your game unless you really have some specific gameplay that need a specific design. It’s always case by case.
Could you please post the link to the thread you mentionned for the discussion on Multicast, I will be interested to read this?