It's surprising right? I like pretty much everything else about them.
To the OP's question: for apps that facilitate micro-transactions I ended up using Stripe, but I forced the user to add a balance to their account first. So, rather than charge their credit card for every micro transaction, they'd add $20.00 to their account in the beginning, and every transaction would just draw-down from that account. Antiquated, but seemed to work alright.