That use case seems to have been entirely superceded by Patreon. The fact that it isn't quite identical, well, that's part of why it has been superceded by Patreon.
But both Flattr and Patreon miss the relatively involuntary nature of ad networks. Certain things can not count on being supported by eager contributors, and need to more-or-less force themselves in to somehow earn revenue. I'm not all that perturbed by saying "then perhaps they shouldn't exist", but I don't have to take a survey to guess I'm in the very minority view on that.
To give a positive example of that where it's not just "clickbait" but is actually a useful thing: My wife and I get a lot of recipes off the internet. But of the several dozen she's pinned on Pinterest, I'd say I've only seen one or two sites repeated. Mostly we're wandering around hither and yon, not showing any site loyalty. If my use case is the common one, then patronage isn't really a solution. (Including Flattr, which to a first approximation, zero of the people visiting those recipe sites have ever heard of, and low single digits of them would use it if they had.) But ads aren't necessarily working terribly well either; I've seen some recipes so laden down with ads that I got tired of waiting for the recipe to stop jumping around on my phone as it loaded Yet Another Ad into the middle of the text, and went and got my computer, where uMatrix nuked the ads without even trying.