Thanks for your review!

however I have found there is a bit of a delay when you receive the notification

That's correct. The server uses the last irreversible block in stead of the last broadcasted block. That gives us more consistent performance, but comes at a price of a delay of around 1 to 2 minutes. Last days might have been a bit longer because of problems with some of the rpc nodes in the network, but it should be all in sync now.