Patreon solved this problem by being developed as a solution to the founder's own problem (getting paid), and priming it with his own fanbase. Do flattr's founders use it for their own creative work?
My problem with patreon is that (from my recollection) everything is a subscription so you are committing to not just a fixed payment now, but a recurring payment to a bunch of different sources. I can't just pay $X/month and have it divided among the recipients that I actually patronized in a given month. Patreon is great for things like supporting a band or podcaster or something there there is not an easy way to tie it back to actual usage, but the recipient has to make a sale up-front.