Great plugin, this is my second purchase (3.9 and 4.0), have a suggestion for you though as an enhancement.
When you write the tracking number back, also write the shipment cost back (postage, insurance).
This makes it much easier to calc P/L for each order.
Secondly, update the Shipping address.
A lot of the times the customer doesn't enter it exactly right, and this will help by updating their account.