I am having trouble with both the contactless chip reader and the plug-in chip and swipe. I work at an outdoor kiosk and use my Android phone's mobile data on Verizon. The contactless reader sometimes likes my phone and sometimes doesn't; when it connects, it's beautiful, but more often than not, it does not connect at all.
I thought the plug-in one would be better, so I got one of those. However, the plug-in chip reader takes minutes to connect (and yes, I keep it charging in between uses so it doesn't lose power)... and when you have a line of small children waiting for facepaint, it's not a good idea to keep them waiting for one parent with a chip card. I have ended up just using the old trusty swiper since it is really fast and works every time.
When I test things out at home, I am connected to our wi-fi and it works quickly and without trouble, but over my mobile data, not so much.
