Even assuming you don't have wifi, it's highly likely that paying for your own dataplan is smarter than going through a third party. GoPago uses Verizon wireless, but does not indicate how much of your monthly fee goes towards it. Small businesses get by on the skin of their teeth, so $1,420 in savings is $1,420 you can spend on something far more important.
I think this breaks down easily: 1) You DO have existing device and data plan, and need to be mobile: Square (or similar service) makes sense. 2) You DONT have existing device or data plan, and need to be mobile: GoPago
I think the evolution of phones tends towards people already carrying a smartphone with data plans, making square (or other service only -- no hardware solutions) somewhat more attractive with its rates.