Blendle co-founder here. I must admit that micropayments sounds exhausting when you think about the model. But we really tried to make the UX very pleasant, and I think we succeeded (and about 1/5 of the users who register take out their credit card and top up, so apparently they agree :)). But, at the same time, prices should be fair. We're always looking at refund percentages to make sure that they stay fair.