I really like the idea of this plugin, but unfortunately it doesn't work.
Or maybe it does, but doesn't for me. I think it is very theme dependent. It will either work with your theme or it will not.
I went through the support forum and found a few similar cases to mine. Big part of each icon is cut off in my theme. James reckons everything works well in his theme, so that's why I get the impression that it depends on the theme you have installed if your payment icons will display correctly or not.
Either way, I am giving 1 star out of 5. Great idea, but from the forums I believe that James knows that the bug is there for several months now, but I see no intention of fixing it ..