I believe that this is mostly because neither of them are available in the U.S. (as far as I know). Every single European service that I tried to use them with

I believe that this is mostly because neither of them are available in the U.S. (as far as I know). Every single European service that I tried to use them with (note: I haven't used plenty of them) accepted them without any issues. As an example, while Amazon.com does not provide the support for them, Amazon.co.uk accepts my Visa Electron card without any issues and I bought a Raspberry Pi using Maestro.