Yeah, for those branded buttons on websites this isn't an alternative. They want all their JavaScript for collect information on the user, even if they don't press the button.

I believe this is to play with (mobile) browser's share button, while even there I don't get how this is supposed to work.

First: How does this figure out where I want to share to? And then: Would it have to load the shared-to page first, parse it to see if there is such a Tag and then interpret it?

Maybe I am missing something.