It's automatic distribution (with the option to also trigger one explicitly if you want). I and many other of your visitors are just about as unlikely to donate to you as to subscribe (well, in my case even more unlikely, since I can't think of any comfortable one-time donation thing I use), so if we use Flattr you can choose to get a piece of our collective pool or nothing from us. Time will tell if it's worth it, but I don't think the framing as an alternative makes sense. None of the things currently in use do the same (except Brave, I haven't kept up what they are doing exactly).