So if your client-base is spending on average less than $15.79 per transaction, then Square yields you more profit. If they're averaging more than $15.79, then looks like Groupon's the way to go.
EDIT: With Mastercard, Visa, and Discover cards, that is.
Can you imagine how many more hackers would try to intercept the Groupon data ? This isn't more convenient, it causes more headaches in the long run. People who lose the device, programs that snoop to listen for number data, phones with the programs get lost, I predict a terrible day for this kind of technology... Trust me ^_^