As I read from the doc of akka,if you send the PoisonPill to one actor,it will stop the actor and it child will stop after the current message has been handled ,so which means the message has not beeen handled in the message box will be lost.
So I think sending the PoisionPill to its only child and watch its death will be fine and nice,by this way,we could still shutdown the supervisor and the handler,but also never lost messages in the handler's mailbox.
In the doc,there are two section ,one in actors and one in router,the description in the router is good documented and we can read that the PoisionPill message are only handled by the router itself and but will still affect its routees,but for the actors the document is not that clear.cause I am not that clear will the parent actor will forward the poisionPill message to its children?I don't think so cause the PoisionPill message and the parent actor's stoping both will cause the child actor stop.
The behavior of this is not well documented ,so I think just send the PoisionPill to its child,here handler actor ,will be fine,and just assume that supervisor as the router's behavior will be fine too.
and this behavior will still give the user more controll to its handler actor too.