I'm a bit surprised at the amount of positive response. This impresses me as rather obnoxious, probably effective, but obnoxious. Something between the pop-over ad and the ever-present network TV promotional crawl brought to the masses.
The message is not showing up for no reason. You clicked a link from someone you follow, because you wanted to usually BECAUSE of how that content relates to them.
Sure, if you just change every link you send out to a link with an ad at the bottom that is bad. But I see no problem with adding context and commentary to a link someone is sharing on social media for that exact reason.