You will get more features using Electrum, such as being able to make a transaction (unsigned) and signing it with your cold storage,...
Also blockchain.info used to let you add watch only addresses, and sending you a free SMS message when you received/sent a transaction.
I would be glad to hear what you thought about my little project, and whether you wanted any specific feature that I could add as improvement.
Just flipping through the
https://bitcoin.org/en/developer-reference#bitcoin-core-apis Remote Procedure Calls, remembering bitcoin-cli allowed simple requests about adresses or transfers send / recieved.
However the existance of some watchonly wallet on GitHub should have told me it isn't that easy.
Can someone confirm if running a bitcoin core client, empty wallet, can enable access to some blockchain explorer alike data? Just things like requesting current ballances associated with any given address (self owned or foreign) or last coin movements required.