I like your tracking app a lot, the carriers are up to date and work fine!
But do you think of implementing multiple carriers for one item, like other tracking apps have?
It often happens that carriers work together, but the main carrier only has "basic" updates.
For example, DHL ships the item, and hands it over to a local delivery carrier (for example bpost). You choose DHL in the start, but when it is handed over to bpost, you only get a notification when the item is delivered, while bpost has a lot of other notifications. When you know it is handed over, you can of course manually change the carrier, but it would be easier if you could choose DHL *and* bpost.
The same goes for a lot of Chinese carriers and PostNL, or it could even be nice to add a secondary tracker like 17track in an item.