I wouldn't trust anything that comes from Mastercard or Visa directly. I would much rather have the companies' idiosyncrasies and politics abstracted through a 3rd-party service like stripe or balanced. That's just my kneejerk reaction, take it or leave it.
On the merchant side, the picture is a lot less friendly than the consumer side. With a traditional merchant account, there is basically a march of monotonically increasing fees here and there that add up, and are only brought back down a bit when someone wins against them in court.
