Always interesting to see different POS concepts. I just wish they would explain the technical details a bit more on their website. What I gather: Some Fig Card central server mediates between the merchant and the smartphone, which - as far as I can tell - needs to be connected to the Internet at the time of the sale.
That requirement would be an issue for some. Personally, I wouldn't want to have to connect to a wi-fi network each time I want to make a payment -- especially a wi-fi netowrk I don't have any reason to trust.
I can't see any reason why they wouldn't want to use the phone's data service instead. It is already established and plenty fast enough for the small amount of data required for a POS transaction.
I'm just not clear on how the app knows in which merchant store the phone currently is. The presentation claims that the phone is not on WiFi, so how else can it tell at what store it is?
I believe Dwolla is using the phone's GPS for knowing the list of merchants nearby: http://www.dwolla.org/help/what-is-dwolla-spots/
That's why I suspect the USB device for the merchant's POS is a wi-fi stick that simply operates as an SSID beacon that the mobile sees so that payment to the correct merchant is ensured. The mobile need not ever connect to to the wi-fi, it just grabs the list of SSIDs from after doing a scan.
But they could be doing anything, who knows.